Light-Emitting Element, Light-Emitting Device, Electronic Device, Lighting Device, and Heterocyclic Compound

ABSTRACT

A light-emitting element with high heat resistance and high emission efficiency is provided. A novel heterocyclic compound that can be used in such a light-emitting element is provided. One embodiment of the present invention is a light-emitting element which includes, between a pair of electrodes, a layer containing a first organic compound, a second organic compound, and a light-emitting substance; the first organic compound includes one pyrimidine ring and one ring with a hole-transport skeleton; the second organic compound is an aromatic amine; and the light-emitting substance converts triplet excitation energy into light. A combination of the first organic compound, which includes the one pyrimidine ring and the one ring with the hole-transport skeleton, and the second organic compound, which is the aromatic amine, forms an exciplex.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light-emitting element, alight-emitting device, an electronic device, a lighting device, and aheterocyclic compound.

2. Description of the Related Art

In recent years, research and development have been extensivelyconducted on light-emitting elements using electroluminescence (EL). Ina basic structure of such a light-emitting element, a layer containing alight-emitting substance is interposed between a pair of electrodes. Byvoltage application to this element, light emission can be obtained fromthe light-emitting substance.

Such a light-emitting element is a self-luminous element and hasadvantages over liquid crystal displays, such as high visibility ofpixels and no need of a backlight; thus, such a light-emitting elementis thought to be suitable as a flat panel display element. Besides, sucha light-emitting element has advantages in that it can be manufacturedto be thin and lightweight, and has very fast response speed.

Furthermore, since such a light-emitting element can be formed in a filmform, the light-emitting element makes it possible to provide planarlight emission; thus, a large-area element utilizing planar lightemission can be easily formed. This feature is difficult to obtain withpoint light sources typified by incandescent lamps and LEDs or linearlight sources typified by fluorescent lamps. Thus, the light-emittingelement also has great potential as a planar light source applicable tolighting and the like.

Such light-emitting elements utilizing electroluminescence can bebroadly classified according to whether a light-emitting substance is anorganic compound or an inorganic compound. In the case of an organic ELelement in which a layer containing an organic compound used as alight-emitting substance is provided between a pair of electrodes,application of voltage to the light-emitting element causes injection ofelectrons from a cathode and holes from an anode into the layercontaining the organic compound having a light-emitting property andthus current flows. The injected electrons and holes then lead theorganic compound having a light-emitting property to its excited state,so that light emission is obtained from the excited organic compoundhaving a light-emitting property.

The excited state formed by an organic compound can be a singlet excitedstate or a triplet excited state. Light emission from the singletexcited state (S*) is called fluorescence, and light emission from thetriplet excited state (T*) is called phosphorescence. Further, thestatistical generation ratio of S* to T* in a light-emitting element isthought to be 1:3.

With a compound that can convert a singlet excited state into light(hereinafter, called a fluorescent compound), only light emission fromthe singlet excited state (fluorescence) is observed and that from thetriplet excited state (phosphorescence) is not observed, at roomtemperature. Accordingly, the internal quantum efficiency (the ratio ofthe number of generated photons to the number of injected carriers) of alight-emitting element including the fluorescent compound is assumed tohave a theoretical limit of 25%, on the basis of S*:T*=1:3.

In contrast, an observation on a compound that can convert a tripletexcited state into light (hereinafter, called a phosphorescent compound)shows light emission from the triplet excited state (phosphorescence).Further, since intersystem crossing (i.e., transition from a singletexcited state to a triplet excited state) easily occurs in aphosphorescent compound, the internal quantum efficiency can betheoretically increased to 75% to 100%. In other words, the emissionefficiency can be three to four times as much as that of a fluorescentcompound. For this reason, light-emitting elements using phosphorescentcompounds have been under active development recently in order thathighly efficient light-emitting elements can be obtained.

When formed using the above-described phosphorescent compound, alight-emitting layer of a light-emitting element is often formed suchthat the phosphorescent compound is dispersed in a matrix containinganother compound in order to suppress concentration quenching orquenching due to triplet-triplet annihilation in the phosphorescentcompound. Here, the compound as the matrix is called a host material,and the compound dispersed in the matrix, such as a phosphorescentcompound, is called a guest material.

In the case where a phosphorescent compound is a guest material, a hostmaterial needs to have higher triplet excitation energy (energydifference between a ground state and a triplet excited state) than thephosphorescent compound.

Furthermore, since singlet excitation energy (energy difference betweena ground state and a singlet excited state) is higher than tripletexcitation energy, a substance that has high triplet excitation energyalso has high singlet excitation energy. Thus, the above substance thathas high triplet excitation energy is also effective in a light-emittingelement using a fluorescent compound as a light-emitting substance.

A compound including pyrimidine or the like has been studied as anelectron-transport material or as a host material in the case where aphosphorescent compound is used as a guest material (e.g., PatentDocument 1).

A compound in which a carbazole skeleton and a nitrogen-containinghetero aromatic ring are combined is disclosed as an example of a hostmaterial in the case where a phosphorescent compound is used as a guestmaterial (e.g., Patent Document 2).

REFERENCE

-   [Patent Document 1] Japanese Published Patent Application No.    2003-45662-   [Patent Document 2] PCT International Publication No. 2011-046182

SUMMARY OF THE INVENTION

As disclosed in Patent Document 1 or Patent Document 2, a host materialfor a phosphorescent compound or a guest material of a phosphorescentcompound has been actively developed. However, a light-emitting elementstill needs to be improved in terms of emission efficiency, reliability,emission characteristics, synthesis efficiency, and cost, and alight-emitting element with better characteristics is expected to bedeveloped.

In view of the above, in one embodiment of the present invention, alight-emitting element which has high heat resistance, low drivevoltage, and a long lifetime is provided. Further, in one embodiment ofthe present invention, a light-emitting element with high heatresistance and high emission efficiency is provided. In one embodimentof the present invention, a novel heterocyclic compound is provided. Byapplication of this novel heterocyclic compound, a light-emittingelement with a long lifetime and a light-emitting element with a longlifetime and high emission efficiency are provided. In one embodiment ofthe present invention, a light-emitting device, an electronic device,and a lighting device each using the light-emitting element areprovided.

Embodiments of the present invention are synthesis of a novelheterocyclic compound with high heat resistance and a light-emittingelement with a long lifetime which uses the obtained novel heterocycliccompound. Another embodiment of the present invention is alight-emitting element which includes a light-emitting layer containinga first organic compound that is the above novel heterocyclic compound,a second organic compound that is another material, and a light-emittingsubstance converting triplet excitation energy into light. A combinationof the first organic compound and the second organic compound allowsgeneration of an exciplex (an excited complex), and with the use ofenergy from the exciplex, the light-emitting substance convertingtriplet excitation energy into light emits light. Note that a differencebetween an S₁ level and a T₁ level of the generated exciplex isextremely small as compared to a difference between an S₁ level and a T₁level of each of the substances (first organic compound and secondorganic compound) before exciplex formation. Thus, an emission spectrumof the exciplex can largely overlap with an absorption spectrum of thelight-emitting substance converting triplet excitation energy intolight, and thus efficiency of energy transfer from a T₁ level of theexciplex to the light-emitting substance converting triplet excitationenergy into light can be increased, which leads to an increase inemission efficiency of a light-emitting element.

That is, one embodiment of the present invention is a light-emittingelement which includes, between a pair of electrodes, a layer containinga first organic compound, a second organic compound, and alight-emitting substance; the first organic compound includes onepyrimidine ring and one ring with a hole-transport skeleton; the secondorganic compound is an aromatic amine; and the light-emitting substanceconverts triplet excitation energy into light. A combination of thefirst organic compound, which includes the one pyrimidine ring and theone ring with the hole-transport skeleton, and the second organiccompound, which is the aromatic amine, forms an exciplex.

Another embodiment of the present invention is a light-emitting elementwhich includes, between a pair of electrodes, a layer containing a firstorganic compound, a second organic compound, and a light-emittingsubstance; the first organic compound includes one pyrimidine ring andone ring with a hole-transport skeleton, and has a molecular weightgreater than or equal to 400 and less than or equal to 1200; the secondorganic compound is an aromatic amine; and the light-emitting substanceconverts triplet excitation energy into light. A combination of thefirst organic compound, which includes the one pyrimidine ring and theone ring with the hole-transport skeleton and has a molecular weightgreater than or equal to 400 and less than or equal to 1200, and thesecond organic compound, which is the aromatic amine, forms an exciplex.

In any of the above structures, as the ring with the hole-transportskeleton included in the first organic compound, a carbazole ring, adibenzothiophene ring, and a dibenzofuran ring can be given.

In any of the above structures, the first organic compound has a highelectron-transport property and thus can be used for anelectron-transport layer, an electron-injection layer, or alight-emitting layer.

In any of the above structures, the ring with the hole-transportskeleton is a carbazole ring, a dibenzothiophene ring, or a dibenzofuranring.

A further embodiment of the present invention is a heterocyclic compoundrepresented by General Formula (G1). Note that the heterocyclic compoundrepresented by General Formula (G1) can be used as the first organiccompound in any of the above structures.

Note that in the formula, Ar¹ to Ar³ separately represent any ofhydrogen, an alkyl group having 1 to 4 carbon atoms, a substituted orunsubstituted phenyl group, and a substituted or unsubstituted biphenylgroup, and R¹ to R³ separately represent any of hydrogen, an alkyl grouphaving 1 to 4 carbon atoms, and a substituted or unsubstituted arylgroup having 6 to 13 carbon atoms. α represents a substituted orunsubstituted phenylene group and n is 2 or 3. Z represents oxygen orsulfur.

In the above structure, the phenylene group represented by α is ano-phenylene group, a m-phenylene group, or a p-phenylene group.

A still further embodiment of the present invention is a heterocycliccompound represented by General Formula (G2). Note that the heterocycliccompound represented by General Formula (G2) can be used as the firstorganic compound in any of the above structures.

Note that in the formula, R¹ to R³ separately represent any of hydrogen,an alkyl group having 1 to 4 carbon atoms, and a substituted orunsubstituted aryl group having 6 to 13 carbon atoms. α represents asubstituted or unsubstituted phenylene group and n is 2 or 3. Zrepresents oxygen or sulfur.

A yet still further embodiment of the present invention is aheterocyclic compound represented by Structural Formula (100). Note thatthe heterocyclic compound represented by Structural Formula (100) isincluded in the categories of the structures represented by GeneralFormula (G1) and General Formula (G2).

A yet still further embodiment of the present invention is aheterocyclic compound represented by Structural Formula (101). Note thatthe heterocyclic compound represented by Structural Formula (101) isincluded in the categories of the structures represented by GeneralFormula (G1) and General Formula (G2).

Since the heterocyclic compounds of embodiments of the present inventionwhich are represented by General Formulae (G1) and (G2) have high heatresistance, by using any of these materials in a light-emitting element,the light-emitting element can have a long lifetime.

Further, the present invention includes, in its scope, electronicdevices and lighting devices including light-emitting devices, as wellas light-emitting devices including light-emitting elements. Thelight-emitting device in this specification refers to an image displaydevice and a light source (e.g., a lighting device). In addition, thelight-emitting device includes, in its category, all of a module inwhich a light-emitting device is connected to a connector such as aflexible printed circuit (FPC) or a tape carrier package (TCP), a modulein which a printed wiring board is provided on the tip of a TCP, and amodule in which an integrated circuit (IC) is directly mounted on alight-emitting element by a chip on glass (COG) method.

In one embodiment of the present invention, a light-emitting elementwhich has high heat resistance, low drive voltage, and a long lifetimecan be provided. Further, in one embodiment of the present invention, alight-emitting element with high heat resistance and high emissionefficiency can be provided. In one embodiment of the present invention,a novel heterocyclic compound can be provided. Note that by applicationof the novel heterocyclic compound, a light-emitting element with highheat resistance and a long lifetime can be provided. In addition, byapplication of the novel heterocyclic compound, a light-emitting elementwith a long lifetime and high emission efficiency can also be provided.Furthermore, in one embodiment of the present invention, alight-emitting device, an electronic device, and a lighting device inwhich power consumption is reduced with the use of the light-emittingelement can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a concept of one embodiment of the present invention.

FIG. 2 illustrates a structure of a light-emitting element.

FIG. 3 illustrates a structure of a light-emitting element.

FIGS. 4A and 4B illustrate structures of light-emitting elements.

FIGS. 5A and 5B illustrate a light-emitting device.

FIGS. 6A to 6D illustrate electronic devices.

FIGS. 7A to 7C illustrate an electronic device.

FIG. 8 illustrates lighting devices.

FIGS. 9A and 9B show ¹H-NMR charts of a heterocyclic compoundrepresented by Structural Formula (100).

FIG. 10 shows results of LC-MS measurement of a heterocyclic compoundrepresented by Structural Formula (100).

FIGS. 11A and 11B show ¹H-NMR charts of a heterocyclic compoundrepresented by Structural Formula (101).

FIG. 12 shows results of LC-MS measurement of a heterocyclic compoundrepresented by Structural Formula (101).

FIG. 13 illustrates a light-emitting element.

FIG. 14 shows current density-luminance characteristics of alight-emitting element 1 and a light-emitting element 2.

FIG. 15 shows voltage-luminance characteristics of a light-emittingelement 1 and a light-emitting element 2.

FIG. 16 shows luminance-current efficiency characteristics of alight-emitting element 1 and a light-emitting element 2.

FIG. 17 shows voltage-current characteristics of a light-emittingelement 1 and a light-emitting element 2.

FIG. 18 shows reliability of a light-emitting element 1 and alight-emitting element 2.

FIG. 19 shows a ¹H-NMR chart of a heterocyclic compound represented byStructural Formula (112).

FIG. 20 shows results of LC-MS measurement of a heterocyclic compoundrepresented by Structural Formula (112).

FIG. 21 shows results of LC-MS measurement of a heterocyclic compoundrepresented by Structural Formula (112).

FIG. 22 shows a ¹H-NMR chart of a heterocyclic compound represented byStructural Formula (121).

FIG. 23 shows results of LC-MS measurement of a heterocyclic compoundrepresented by Structural Formula (121).

FIG. 24 shows current density-luminance characteristics of alight-emitting element 3 and a light-emitting element 4.

FIG. 25 shows voltage-luminance characteristics of a light-emittingelement 3 and a light-emitting element 4.

FIG. 26 shows luminance-current efficiency characteristics of alight-emitting element 3 and a light-emitting element 4.

FIG. 27 shows voltage-current characteristics of a light-emittingelement 3 and a light-emitting element 4.

FIG. 28 shows reliability of a light-emitting element 4.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the present invention will be described withreference to the drawings. Note that the present invention is notlimited to the following description, and modes and details thereof canbe modified in various ways without departing from the spirit and scopeof the invention. Thus, the present invention should not be construed asbeing limited to the description in the following embodiments.

Embodiment 1

In this embodiment, heterocyclic compounds each of which is oneembodiment of the present invention will be described.

The heterocyclic compound that is one embodiment of the presentinvention includes one pyrimidine ring and one ring with ahole-transport skeleton. Note that the heterocyclic compound in thisembodiment which includes one pyrimidine ring and one ring with ahole-transport skeleton has a structure represented by General Formula(G1).

In General Formula (G1), Ar¹ to Ar³ separately represent any ofhydrogen, an alkyl group having 1 to 4 carbon atoms, a substituted orunsubstituted phenyl group, and a substituted or unsubstituted biphenylgroup, and R¹ to R³ separately represent any of hydrogen, an alkyl grouphaving 1 to 4 carbon atoms, and a substituted or unsubstituted arylgroup having 6 to 13 carbon atoms. α represents a substituted orunsubstituted phenylene group and n is 2 or 3. Z represents oxygen orsulfur. Note that the phenylene group represented by α is an o-phenylenegroup, a in-phenylene group, or a p-phenylene group.

Note that the heterocyclic compound that is one embodiment of thepresent invention preferably has a structure represented by GeneralFormula (G2) where two of Ar¹ to Ar³ in General Formula (G1) representphenyl groups and the other represents hydrogen, in which case synthesiscan be facilitated.

Note that in General Formula (G2), R¹ to R³ separately represent any ofhydrogen, an alkyl group having 1 to 4 carbon atoms, and a substitutedor unsubstituted aryl group having 6 to 13 carbon atoms. α represents asubstituted or unsubstituted phenylene group and n is 2 or 3. Zrepresents oxygen or sulfur.

As specific structures of (α)_(n) (where n is 2 or 3) in General Formula(G1) or (G2), there are substituents represented by Structural Formulae(1-1) to (1-4), for example.

As specific structures of Ar¹ to Ar³ and R¹ to R³ in General Formula(G1) or (G2), there are substituents represented by Structural Formulae(2-1) to (2-19), for example.

As specific examples of the heterocyclic compound that can be used forone embodiment of the present invention, there are heterocycliccompounds represented by Structural Formulae (100) to (120). However, itis to be noted that the present invention is not limited to these.

A variety of reactions can be applied as a method for synthesizing anyof the heterocyclic compounds of embodiments of the present invention.For example, reactions described below enable the synthesis of theheterocyclic compound of one embodiment of the present inventionrepresented by General Formula (G1). Note that the methods forsynthesizing the heterocyclic compound of one embodiment of the presentinvention are not limited to the synthesis methods below.

<<Method for Synthesizing Heterocyclic Compound Represented by GeneralFormula (G1)>>

Synthesis Scheme (A) of the heterocyclic compound represented by GeneralFormula (G1) is shown below.

In General Formula (G1), Ar¹ to Ar^(a) separately represent any ofhydrogen, an alkyl group having 1 to 4 carbon atoms, a substituted orunsubstituted phenyl group, and a substituted or unsubstituted biphenylgroup, and R¹ to R³ separately represent any of hydrogen, an alkyl grouphaving 1 to 4 carbon atoms, and a substituted or unsubstituted arylgroup having 6 to 13 carbon atoms. α represents a substituted orunsubstituted phenylene group and n is 2 or 3. Z represents oxygen orsulfur.

As shown in Synthesis Scheme (A), the heterocyclic compound representedby General Formula (G1) can be obtained by making a halide of apyrimidine derivative (a1) react with a boronic acid compound ofdibenzothiophene, a derivative thereof, dibenzofuran, or a derivativethereof (a2). Note that X in the formula represents a halogen element.P¹ and P² each represent a substituted or unsubstituted phenylene group.l+m equals n, which is 2 or 3. B¹ represents a boronic acid, a boronicester, a cyclic-triolborate salt, or the like. As the cyclic-triolboratesalt, a lithium salt, a potassium salt, or a sodium salt may be used.

Note that a boronic acid compound of a pyrimidine derivative may bereacted with a halide of dibenzothiophene, a derivative thereof,dibenzofuran, or a derivative thereof.

Note that since a wide variety of the compounds (a1) and (a2) arecommercially available or their synthesis is feasible, a great varietyof the pyrimidine derivative represented by General Formula (G1) can besynthesized. Thus, a feature of the heterocyclic compound which is oneembodiment of the present invention is the abundance of variations.

Thus, the heterocyclic compound that is one embodiment of the presentinvention can be synthesized.

Since the heterocyclic compounds in this embodiment that are embodimentsof the present invention have high heat resistance, by fabricating alight-emitting element with the use of any of these materials, thelight-emitting element can have a long lifetime. Further, since theheterocyclic compounds that are embodiments of the present inventionhave high electron-transport properties, any of the heterocycliccompounds can be suitably used as a material for an electron-injectionlayer, an electron-transport layer, or a light-emitting layer in alight-emitting element. Furthermore, when the heterocyclic compound thatis one embodiment of the present invention is combined with anothermaterial to form an exciplex in a light-emitting element, thelight-emitting element can have a long lifetime and high emissionefficiency.

Embodiment 2

In this embodiment, a concept and a specific structure of alight-emitting element which utilizes an exciplex and to which any ofthe heterocyclic compounds of embodiments of the present inventiondescribed in Embodiment 1 is applied will be described.

Note that a light-emitting element described in this embodimentincludes, between a pair of electrodes, a light-emitting layer whichcontains a first organic compound, a second organic compound, and alight-emitting substance converting triplet excitation energy intolight. A combination of the first organic compound and the secondorganic compound can form an exciplex, and in the light-emitting layer,the light-emitting substance converting triplet excitation energy intolight emits light owing to energy transfer from the exciplex.

Here, a process of exciplex formation in a light-emitting layer of alight-emitting element of one embodiment of the present invention willbe described. There are two possible formation processes, which aredescribed below.

In one process, an exciplex is formed from the first organic compoundwith an electron-transport property (e.g., a host material) and thesecond organic compound with a skeleton represented by General Formula(G1) which have carriers (cation or anion). Note that in such aformation process, formation of a singlet exciton from the first organiccompound and the second organic compound can be suppressed, whichenables the light-emitting element to have a long lifetime.

The other formation process is an elementary process where one of thefirst organic compound with an electron-transport property (e.g., a hostmaterial) and the second organic compound with the skeleton representedby General Formula (G1) forms a singlet exciton and then interacts withthe other in a ground state to form an exciplex. In this case, althoughthe first organic compound or the second organic compound is broughtinto a singlet excited state at first, the singlet excited state israpidly converted into an exciplex; thus, deactivation of the singletexcitation energy, reaction from the singlet excited state, and the likecan be suppressed also in this case, so that the light-emitting elementcan have a long lifetime.

Note that in a light-emitting element that is one embodiment of thepresent invention, an exciplex may be formed in either of the twoformation processes.

FIG. 1 shows formation of levels of an exciplex which is formed throughthe above formation process, and a process for light emission in alight-emitting layer of a light-emitting element that is one embodimentof the present invention. As shown in FIG. 1, a difference between an S₁level and a T₁ level of an exciplex 10 formed in the light-emittinglayer of the light-emitting element is extremely small as compared to adifference between an S₁ level and a T₁ level of each of the substances(first organic compound and second organic compound) before exciplexformation. Thus, when an absorption spectrum of a light-emittingsubstance 11 which is contained in the light-emitting layer and convertstriplet excitation energy into light largely overlaps with an emissionspectrum of the exciplex formed in the light-emitting layer, not only T₁energy but also S₁ energy generated in the exciplex can be efficientlytransferred to the light-emitting substance which converts tripletexcitation energy into light. As a result, emission efficiency of thelight-emitting element can be considerably enhanced.

Next, a structure of a light-emitting element that is one embodiment ofthe present invention will be described with reference to FIG. 2.

As illustrated in FIG. 2, the light-emitting element that is oneembodiment of the present invention includes, between a pair ofelectrodes (an anode 101 and a cathode 102), a light-emitting layer 104which contains a first organic compound 105, a second organic compound106, and a light-emitting substance 107; the first organic compound 105includes one pyrimidine ring and one ring with a hole-transportskeleton; the second organic compound 106 is an aromatic amine; and thelight-emitting substance 107 converts triplet excitation energy intolight. The light-emitting layer 104 is one of functional layers includedin an EL layer 103 which is in contact with the pair of electrodes. TheEL layer 103 can include, in addition to the light-emitting layer 104,any of a hole-injection layer, a hole-transport layer, anelectron-transport layer, an electron-injection layer, and the like asappropriate at given positions.

The first organic compound 105, which includes the one pyrimidine ringand the one ring with the hole-transport skeleton, is a heterocycliccompound that is one embodiment of the present invention and has thestructure represented by General Formula (G1).

In the formula, Ar¹ to Ar³ separately represent any of hydrogen, analkyl group having 1 to 4 carbon atoms, a substituted or unsubstitutedphenyl group, and a substituted or unsubstituted biphenyl group, and R¹to R³ separately represent any of hydrogen, an alkyl group having 1 to 4carbon atoms, and a substituted or unsubstituted aryl group having 6 to13 carbon atoms. α represents a substituted or unsubstituted phenylenegroup and n is 2 or 3. Z represents oxygen or sulfur.

Note that Embodiment 1 can be referred to for specific examples of thefirst organic compound represented by General Formula (G1); thus, thedescription is not repeated here.

The following are examples of the second organic compound 106 that is anaromatic amine: a compound having an aromatic amine skeleton such as4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB),N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(abbreviation: TPD),4,4′-bis[N-(Spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB), 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine(abbreviation: BPAFLP), 4-phenyl-3′-(9-phenylfluoren-9-yl)triphenylamine(abbreviation: mBPAFLP),4-phenyl-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation:PCBA1BP), 4,4′-diphenyl-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBBi1BP),4-(1-naphthyl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBANB),4,4′-di(1-naphthyl)-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBNBB),9,9-dimethyl-N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]fluoren-2-amine(abbreviation: PCBAF), orN-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]Spiro-9,9′-bifluoren-2-amine (abbreviation: PCBASF); and a compoundhaving a carbazole skeleton such as 1,3-bis(N-carbazolyl)benzene(abbreviation: mCP), 4,4′-di(N-carbazolyl)biphenyl (abbreviation: CBP),3,6-bis(3,5-diphenylphenyl)-9-phenylcarbazole (abbreviation: CzTP), or3,3′-bis(9-phenyl-9H-carbazole) (abbreviation: PCCP).

Note that the first organic compound 105 and the second organic compound106 are not limited to the above substances as long as a combination ofthe first organic compound 105 and the second organic compound 106 canform an exciplex.

Further, as the light-emitting substance 107 which converts tripletexcitation energy into light, a phosphorescent compound (e.g., anorganometallic complex), a thermally activated delayed fluorescence(TADF) material, or the like is preferably used.

Note that examples of the organometallic complex includebis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)tetrakis(1-pyrazolyl)borate (abbreviation: FIr6),bis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III) picolinate(abbreviation: FIrpic),bis{2-[3′,5′-bis(trifluoromethyl)phenyl]pyridinato-N,C^(2′)}iridium(III)picolinate (abbreviation: Ir(CF₃ppy)₂(pic)),bis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)acetylacetonate (abbreviation: FIracac),tris(2-phenylpyridinato)iridium(III) (abbreviation: Ir(ppy)₃),bis(2-phenylpyridinato)iridium(III) acetylacetonate (abbreviation:Ir(ppy)₂(acac)), bis(benzo[h]quinolinato)iridium(III) acetylacetonate(abbreviation: Ir(bzq)₂(acac)),bis(2,4-diphenyl-1,3-oxazolato-N,C^(2′))iridium(III) acetylacetonate(abbreviation: Ir(dpo)₂(acac)),bis{2-[4′-(perfluorophenyl)phenyl]pyridinato-N,C^(2′)}iridium(III)acetylacetonate (abbreviation: Ir(p-PF-ph)₂(acac)),bis(2-phenylbenzothiazolato-N,C^(2′))iridium(III) acetylacetonate(abbreviation: Ir(bt)₂(acac)),bis[2-(2′-benzo[4,5-α]thienyl)pyridinato-N,C^(3′)]iridium(III)acetylacetonate (abbreviation: Ir(btp)₂(acac)),bis(1-phenylisoquinolinato-N,C^(2′))iridium(III) acetylacetonate(abbreviation: Ir(piq)₂(acac)),(acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III)(abbreviation: Ir(Fdpq)₂(acac)),(acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III)(abbreviation: Ir(tppr)₂(acac)),2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin platinum(II)(abbreviation: PtOEP),tris(acetylacetonato)(monophenanthroline)terbium(III) (abbreviation:Tb(acac)₃(Phen)),tris(1,3-diphenyl-1,3-propanedionato)(monophenanthroline)europium(III)(abbreviation: Eu(DBM)₃(Phen)), and tris[1-(2-thenoyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(III)(abbreviation: Eu(TTA)₃(Phen)).

In the light-emitting element in this embodiment that is one embodimentof the present invention, a heterocyclic compound with high heatresistance that is one embodiment of the present invention is used forthe light-emitting layer; moreover, the combination of the heterocycliccompound and the second organic compound that is an aromatic amine canform an exciplex in the light-emitting layer. Accordingly, efficiency ofenergy transfer from the exciplex to the light-emitting substanceconverting triplet excitation energy into light can be increased, sothat the light-emitting element can have a long lifetime and highemission efficiency.

Embodiment 3

In this embodiment, an example of a light-emitting element in oneembodiment of the present invention is described with reference to FIG.3.

In the light-emitting element described in this embodiment, asillustrated in FIG. 3, an EL layer 203 including a light-emitting layer206 is provided between a pair of electrodes (a first electrode (anode)201 and a second electrode (cathode) 202), and the EL layer 203 includesa hole-injection layer 204, a hole-transport layer 205, anelectron-transport layer 207, an electron-injection layer 208, and thelike in addition to the light-emitting layer 206.

In a manner similar to that of the light-emitting element described inEmbodiment 2, the light-emitting layer 206 includes a first organiccompound 209 that is a heterocyclic compound described in Embodiment 1,a second organic compound 210 that is an aromatic amine, and alight-emitting substance 211 converting triplet excitation energy intolight. Since any of the substances described in Embodiments 1 and 2 canbe used for the first organic compound 209, the second organic compound210, and the light-emitting substance 211 converting triplet excitationenergy into light, the description thereof is not repeated here.

For the first electrode (anode) 201 and the second electrode (cathode)202, a metal, an alloy, an electrically conductive compound, a mixturethereof, or the like can be used. Specifically, indium oxide-tin oxide(ITO: indium tin oxide), indium oxide-tin oxide containing silicon orsilicon oxide, indium oxide-zinc oxide (indium zinc oxide), indium oxidecontaining tungsten oxide and zinc oxide, gold (Au), platinum (Pt),nickel (Ni), tungsten (W), chromium (Cr), molybdenum (Mo), iron (Fe),cobalt (Co), copper (Cu), palladium (Pd), or titanium (Ti) can be used.In addition, an element belonging to Group 1 or Group 2 of the periodictable, for example, an alkali metal such as lithium (Li) or cesium (Cs),an alkaline earth metal such as magnesium (Mg), calcium (Ca), orstrontium (Sr), an alloy containing such an element (e.g., MgAg orAlLi), a rare earth metal such as europium (Eu) or ytterbium (Yb), analloy containing such an element, graphene, or the like can be used. Thefirst electrode (anode) 201 and the second electrode (cathode) 202 canbe formed by, for example, a sputtering method, an evaporation method(including a vacuum evaporation method), or the like.

Examples of a substance having a high hole-transport property which isused for the hole-injection layer 204 and the hole-transport layer 205include aromatic amine compounds such as4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB orα-NPD),N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(abbreviation: TPD), 4,4′,4″-tris(carbazol-9-yl)triphenylamine(abbreviation: TCTA), 4,4′,4″-tris(N,N-diphenylamino)triphenylamine(abbreviation: TDATA),4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine(abbreviation: MTDATA), and4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB),3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA1),3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA2), and3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole(abbreviation: PCzPCN1). Other examples include carbazole derivativessuch as 4,4′-di(N-carbazolyl)biphenyl (abbreviation: CBP),1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbreviation: TCPB), and9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole (abbreviation: CzPA).The substances mentioned here are mainly substances that have a holemobility of 10⁻⁶ cm²/Vs or more. Note that other than these substances,any substance that has a hole-transport property higher than anelectron-transport property may be used.

Still other examples include high molecular compounds such aspoly(N-vinylcarbazole) (abbreviation: PVK), poly(4-vinyltriphenylamine)(abbreviation: PVTPA), poly[N-(4-{N′-[4-(4-diphenylamino)phenyl]phenyl-N′-phenylamino}phenyl)methacrylamide](abbreviation: PTPDMA), andpoly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (abbreviation:Poly-TPD).

Further, examples of an acceptor substance which can be used for thehole-injection layer 204 include oxides of transition metals, oxides ofmetals belonging to Groups 4 to 8 of the periodic table, and the like.Specifically, molybdenum oxide is particularly preferable.

As described above, the light-emitting layer 206 includes the firstorganic compound 209 with an electron-transport property and the secondorganic compound 210 with the skeleton represented by General Formula(G 1) (and may further include a light-emitting substance convertingtriplet excitation energy into light).

The electron-transport layer 207 is a layer that contains a substancehaving a high electron-transport property. For the electron-transportlayer 207, it is possible to use a metal complex such as Alq₃,tris(4-methyl-8-quinolinolato)aluminum (abbreviation: Almq₃),bis(10-hydroxybenzo[h]quinolinato)beryllium (abbreviation: BeBq₂), BAlq,Zn(BOX)₂, or bis[2-(2-hydroxyphenyl)benzothiazolato]zinc (abbreviation:Zn(BTZ)₂). Alternatively, it is possible to use a heteroaromaticcompound such as2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),3-(4′-tert-butylphenyl)-4-phenyl-5-(4″-biphenyl)-1,2,4-triazole(abbreviation: TAZ),3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole(abbreviation: p-EtTAZ), bathophenanthroline (abbreviation: BPhen),bathocuproine (abbreviation: BCP), or4,4′-bis(5-methylbenzoxazol-2-yl)stilbene (abbreviation: BzOs). Furtheralternatively, it is possible to use a high molecular compound such aspoly(2,5-pyridinediyl) (abbreviation: PPy),poly[(9,9-dihexylfluorene-2,7-diyl)-co-(pyridine-3,5-diyl)](abbreviation: PF-Py), orpoly[(9,9-dioctylfluorene-2,7-diyl)-co-(2,2′-bipyridine-6,6′-diyl)](abbreviation: PF-BPy). The substances mentioned here are mainlysubstances that have an electron mobility of 10⁻⁶ cm²/Vs or more. Notethat other than these substances, any substance that has anelectron-transport property higher than a hole-transport property may beused for the electron-transport layer 207.

The electron-transport layer 207 is not limited to a single layer, andmay be a stack of two or more layers containing any of the abovesubstances.

The electron-injection layer 208 is a layer that contains a substancehaving a high electron-injection property. Examples of the substancethat can be used for the electron-injection layer 208 include alkalimetals, alkaline earth metals, and compounds thereof, such as lithiumfluoride (LiF), cesium fluoride (CsF), calcium fluoride (CaF₂), andlithium oxide (LiO_(x)), and rare earth metal compounds, such as erbiumfluoride (ErF₃). Alternatively, the above-mentioned substances forforming the electron-transport layer 207 can be used.

Alternatively, a composite material in which an organic compound and anelectron donor (a donor) are mixed may be used for theelectron-injection layer 208. Such a composite material, in whichelectrons are generated in the organic compound by the electron donor,has high electron-injection and electron-transport properties. Theorganic compound here is preferably a material excellent in transportingthe generated electrons, and specifically any of the above substances(such as metal complexes and heteroaromatic compounds) for theelectron-transport layer 207 can be used. As the electron donor, asubstance showing an electron-donating property with respect to theorganic compound may be used. Specifically, alkali metals, alkalineearth metals, and rare earth metals are preferable, and lithium, cesium,magnesium, calcium, erbium, ytterbium, and the like can be given. Any ofalkali metal oxides and alkaline earth metal oxides is preferable,examples of which are lithium oxide, calcium oxide, barium oxide, andthe like, and a Lewis base such as magnesium oxide or an organiccompound such as tetrathiafulvalene (abbreviation: TTF) can be used.

Note that the hole-injection layer 204, the hole-transport layer 205,the light-emitting layer 206, the electron-transport layer 207, and theelectron-injection layer 208 which are mentioned above can each beformed by a method such as an evaporation method (including a vacuumevaporation method), an inkjet method, or a coating method.

Light emission obtained in the light-emitting layer 206 of theabove-described light-emitting element is extracted to the outsidethrough either the first electrode 201 or the second electrode 202 orboth. Thus, either the first electrode 201 or the second electrode 202in this embodiment, or both, is an electrode having a light-transmittingproperty.

In the light-emitting layer of the light-emitting element in thisembodiment, an exciplex is generated from the first organic compound209, which is a heterocyclic compound of one embodiment of the presentinvention, and the second organic compound 210. Efficiency of energytransfer from the generated exciplex to the light-emitting substance 211converting triplet excitation energy into light can be increased, sothat the light-emitting element can have a long lifetime and highemission efficiency.

Note that the light-emitting element described in this embodiment is oneembodiment of the present invention and is particularly characterized bythe structure of the light-emitting layer. Thus, when the structuredescribed in this embodiment is employed, a passive matrixlight-emitting device, an active matrix light-emitting device, and thelike can be manufactured. Each of these light-emitting devices isincluded in the present invention.

Note that there is no particular limitation on the structure of a TFT inthe case of manufacturing the active matrix light-emitting device. Forexample, a staggered TFT or an inverted staggered TFT can be used asappropriate. Further, a driver circuit formed over a TFT substrate maybe formed using both an n-type TFT and a p-type TFT or either an n-typeTFT or a p-type TFT. Furthermore, there is also no particular limitationon the crystallinity of a semiconductor film used for the TFT. Forexample, an amorphous semiconductor film, a crystalline semiconductorfilm, an oxide semiconductor film, or the like can be used.

Note that the structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

Embodiment 4

In this embodiment, as one embodiment of the present invention, alight-emitting element (hereinafter referred to as tandem light-emittingelement) in which a charge generation layer is provided between aplurality of EL layers will be described.

The light-emitting element described in this embodiment is a tandemlight-emitting element including a plurality of EL layers (a first ELlayer 302(1) and a second EL layer 302(2)) between a pair of electrodes(a first electrode 301 and a second electrode 304) as illustrated inFIG. 4A.

In this embodiment, the first electrode 301 functions as an anode, andthe second electrode 304 functions as a cathode. Note that the firstelectrode 301 and the second electrode 304 can have structures similarto those described in Embodiment 1. In addition, all or any of theplurality of EL layers (the first EL layer 302(1) and the second ELlayer 302(2)) may have structures similar to those described inEmbodiment 1 or 2. In other words, the structures of the first EL layer302(1) and the second EL layer 302(2) may be the same or different fromeach other and can be similar to those of the EL layers described inEmbodiment 1 or 2.

Further, a charge generation layer 305 is provided between the pluralityof EL layers (the first EL layer 302(1) and the second EL layer 302(2)).The charge generation layer 305 has a function of injecting electronsinto one of the EL layers and injecting holes into the other of the ELlayers when voltage is applied between the first electrode 301 and thesecond electrode 304. In this embodiment, when voltage is applied suchthat the potential of the first electrode 301 is higher than that of thesecond electrode 304, the charge generation layer 305 injects electronsinto the first EL layer 302(1) and injects holes into the second ELlayer 302(2).

Note that in terms of light extraction efficiency, the charge generationlayer 305 preferably has a light-transmitting property with respect tovisible light (specifically, the charge generation layer 305 preferablyhas a visible light transmittance of 40% or more). Further, the chargegeneration layer 305 functions even if it has lower conductivity thanthe first electrode 301 or the second electrode 304.

The charge generation layer 305 may have either a structure in which anelectron acceptor (acceptor) is added to an organic compound having ahigh hole-transport property or a structure in which an electron donor(donor) is added to an organic compound having a high electron-transportproperty. Alternatively, both of these structures may be stacked.

In the case where the electron acceptor is added to the organic compoundhaving a high hole-transport property, examples of the organic compoundhaving a high hole-transport property include aromatic amine compoundssuch as NPB, TPD, TDATA, MTDATA, and4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino] biphenyl(abbreviation: BSPB), and the like. The substances mentioned here aremainly substances that have a hole mobility of 10⁻⁶ cm²/Vs or more. Notethat other than these substances, any organic compound that has ahole-transport property higher than an electron-transport property maybe used.

Examples of the electron acceptor include7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation:F₄-TCNQ), chloranil, oxides of transition metals, and oxides of metalsthat belong to Groups 4 to 8 of the periodic table. Specifically,vanadium oxide, niobium oxide, tantalum oxide, chromium oxide,molybdenum oxide, tungsten oxide, manganese oxide, and rhenium oxide arepreferable because of their high electron-accepting property. Amongthese, molybdenum oxide is especially preferable since it is stable inthe air, has a low hygroscopic property, and is easy to handle.

On the other hand, in the case where the electron donor is added to theorganic compound having a high electron-transport property, examples ofthe organic compound having a high electron-transport property which canbe used are metal complexes having a quinoline skeleton or abenzoquinoline skeleton, such as Alq, Almq₃, BeBq₂, and BAlq, and thelike. Other examples are metal complexes having an oxazole-based orthiazole-based ligand, such as Zn(BOX)₂ and Zn(BTZ)₂. Other than metalcomplexes, PBD, OXD-7, TAZ, BPhen, BCP, or the like can be used. Thesubstances mentioned here are mainly substances that have an electronmobility of 10⁻⁶ cm²/Vs or more. Note that other than these substances,any organic compound that has an electron-transport property higher thana hole-transport property may be used.

Examples of the electron donor which can be used are alkali metals,alkaline earth metals, rare earth metals, metals that belong to Group 13of the periodic table, and oxides or carbonates thereof. Specifically,lithium (Li), cesium (Cs), magnesium (Mg), calcium (Ca), ytterbium (Yb),indium (In), lithium oxide, cesium carbonate, and the like arepreferable. An organic compound, such as tetrathianaphthacene, may beused as the electron donor.

Note that forming the charge generation layer 305 by using any of theabove materials can suppress a drive voltage increase caused by thestack of the EL layers.

Although this embodiment shows the light-emitting element having two ELlayers, the present invention can be similarly applied to alight-emitting element in which n EL layers (n is 3 or more) are stackedas illustrated in FIG. 4B. In the case where a plurality of EL layersare included between a pair of electrodes as in the light-emittingelement in this embodiment, by provision of the charge generation layersbetween the EL layers, light emission in a high luminance region can beobtained with current density kept low. Since the current density can bekept low, the element can have a long lifetime. When the light-emittingelement is applied to lighting, voltage drop due to resistance of anelectrode material can be reduced, thereby achieving homogeneous lightemission in a large area. Moreover, it is possible to achieve alight-emitting device which can be driven at low voltage and has lowpower consumption.

Furthermore, by making emission colors of EL layers different, light ofa desired color can be obtained from the light-emitting element as awhole. For example, the emission colors of first and second EL layersare complementary in a light-emitting element having the two EL layers,so that the light-emitting element can be made to emit white light as awhole. Note that the term “complementary” means color relationship inwhich an achromatic color is obtained when colors are mixed. That is,emission of white light can be obtained by mixture of light emitted fromsubstances whose emission colors are complementary colors.

Further, the same applies to a light-emitting element having three ELlayers. For example, the light-emitting element as a whole can emitwhite light when the emission color of the first EL layer is red, theemission color of the second EL layer is green, and the emission colorof the third EL layer is blue.

As well as the structure in this embodiment in which the EL layers arestacked with the charge generation layer provided therebetween, thelight-emitting element may have a micro optical resonator (microcavity)structure which utilizes a light resonant effect by adjusting a distancebetween the electrodes (the first electrode 301 and the second electrode304) to a desired value.

Note that the structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

Embodiment 5

In this embodiment, a light-emitting device including a light-emittingelement which is one embodiment of the present invention will bedescribed.

Note that any of the light-emitting elements described in the otherembodiments can be used as the light-emitting element. Further, althougheither of a passive matrix light-emitting device and an active matrixlight-emitting device may be used as the light-emitting device, anactive matrix light-emitting device will be described in this embodimentwith reference to FIGS. 5A and 5B.

Note that FIG. 5A is a top view illustrating a light-emitting device andFIG. 5B is a cross-sectional view taken along the chain line A-A′ inFIG. 5A. The active matrix light-emitting device in this embodimentincludes a pixel portion 502 provided over an element substrate 501, adriver circuit portion (a source line driver circuit) 503, and drivercircuit portions (gate line driver circuits) 504 a and 504 b. The pixelportion 502, the driver circuit portion 503, and the driver circuitportions 504 a and 504 b are sealed between the element substrate 501and a sealing substrate 506 with a sealant 505.

In addition, there is provided a lead wiring 507 over the elementsubstrate 501. The lead wiring 507 is provided for connecting anexternal input terminal through which a signal (e.g., a video signal, aclock signal, a start signal, or a reset signal) or a potential from theoutside is transmitted to the driver circuit portion 503 and the drivercircuit portions 504 a and 504 b. Here is shown an example in which aflexible printed circuit (FPC) 508 is provided as the external inputterminal. Although only the FPC is illustrated, this FPC may be providedwith a printed wiring board (PWB). The light-emitting device in thisspecification includes, in its category, not only the light-emittingdevice itself but also the light-emitting device provided with the FPCor the PWB.

Next, a cross-sectional structure is described with reference to FIG.5B. The driver circuit portions and the pixel portion are formed overthe element substrate 501; here are illustrated the driver circuitportion 503 which is the source line driver circuit and the pixelportion 502.

The driver circuit portion 503 is an example where a CMOS circuit isformed, which is a combination of an n-channel TFT 509 and a p-channelTFT 510. Note that a circuit included in the driver circuit portion maybe formed using any of various circuits, such as a CMOS circuit, a PMOScircuit, or an NMOS circuit. Although a driver-integrated type in whicha driver circuit is formed over the substrate is described in thisembodiment, the present invention is not limited to this type, and thedriver circuit can be formed outside the substrate.

The pixel portion 502 includes a plurality of pixels each of whichincludes a switching TFT 511, a current control TFT 512, and a firstelectrode (anode) 513 which is electrically connected to a wiring (asource electrode or a drain electrode) of the current control TFT 512.Note that an insulator 514 is formed to cover end portions of the firstelectrode (anode) 513. In this embodiment, the insulator 514 is formedusing a positive photosensitive acrylic resin.

The insulator 514 preferably has a curved surface with curvature at anupper end portion or a lower end portion thereof in order to obtainfavorable coverage by a film which is to be stacked over the insulator514. For example, in the case of using a positive photosensitive acrylicresin as a material for the insulator 514, the insulator 514 preferablyhas a curved surface with a curvature radius (0.2 μm to 3 μm) at theupper end portion. The insulator 514 can be formed using either anegative photosensitive resin or a positive photosensitive resin. Thematerial of the insulator 514 is not limited to an organic compound andan inorganic compound such as silicon oxide or silicon oxynitride canalso be used.

An EL layer 515 and a second electrode (cathode) 516 are stacked overthe first electrode (anode) 513, so that a light-emitting element 517 isformed. Note that the EL layer 515 includes at least the light-emittinglayer described in Embodiment 1. Further, in the EL layer 515, ahole-injection layer, a hole-transport layer, an electron-transportlayer, an electron-injection layer, a charge generation layer, and thelike can be provided as appropriate in addition to the light-emittinglayer.

For the first electrode (anode) 513, the EL layer 515, and the secondelectrode (cathode) 516, the materials described in Embodiment 2 can beused. Although not illustrated, the second electrode (cathode) 516 iselectrically connected to the FPC 508 which is an external inputterminal.

Although the cross-sectional view in FIG. 5B illustrates only onelight-emitting element 517, a plurality of light-emitting elements arearranged in a matrix in the pixel portion 502. Light-emitting elementswhich provide three kinds of light emission (R, and B) are selectivelyformed in the pixel portion 502, whereby a light-emitting device capableof full color display can be fabricated. Alternatively, a light-emittingdevice capable of full color display may be fabricated by a combinationwith color filters.

Further, the sealing substrate 506 is attached to the element substrate501 with the sealant 505, whereby the light-emitting element 517 isprovided in a space 518 surrounded by the element substrate 501, thesealing substrate 506, and the sealant 505. The space 518 may be filledwith an inert gas (such as nitrogen or argon) or the sealant 505.

An epoxy-based resin is preferably used for the sealant 505. It ispreferable that such a material do not transmit moisture or oxygen asmuch as possible. As the sealing substrate 506, a glass substrate, aquartz substrate, or a plastic substrate formed of fiberglass reinforcedplastic (FRP), poly(vinyl fluoride) (PVF), polyester, acrylic, or thelike can be used.

As described above, an active matrix light-emitting device can beobtained.

Note that the structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

Embodiment 6

In this embodiment, examples of a variety of electronic devices whichare completed using a light-emitting device will be described withreference to FIGS. 6A to 6D and FIGS. 7A to 7C. The light-emittingdevice is fabricated using a light-emitting element which is oneembodiment of the present invention.

Examples of electronic devices to which the light-emitting device isapplied are television devices (also referred to as TV or televisionreceivers), monitors for computers and the like, cameras such as digitalcameras and digital video cameras, digital photo frames, cellular phones(also referred to as mobile phones or mobile phone devices), portablegame machines, portable information terminals, audio playback devices,large game machines such as pin-ball machines, and the like. Specificexamples of these electronic devices are illustrated in FIGS. 6A to 6D.

FIG. 6A illustrates an example of a television device. In a televisiondevice 7100, a display portion 7103 is incorporated in a housing 7101.The display portion 7103 is capable of displaying images, and thelight-emitting device can be used for the display portion 7103. Inaddition, here, the housing 7101 is supported by a stand 7105.

The television device 7100 can be operated with an operation switchprovided in the housing 7101 or a separate remote controller 7110. Withoperation keys 7109 of the remote controller 7110, channels and volumecan be controlled and images displayed on the display portion 7103 canbe controlled. Furthermore, the remote controller 7110 may be providedwith a display portion 7107 for displaying data output from the remotecontroller 7110.

Note that the television device 7100 is provided with a receiver, amodem, and the like. With the receiver, general television broadcastingcan be received. Furthermore, when the television device 7100 isconnected to a communication network by wired or wireless connection viathe modem, one-way (from a transmitter to a receiver) or two-way(between a transmitter and a receiver, between receivers, or the like)data communication can be performed.

FIG. 6B illustrates a computer, which includes a main body 7201, ahousing 7202, a display portion 7203, a keyboard 7204, an externalconnection port 7205, a pointing device 7206, and the like. Note thatthis computer is manufactured by using the light-emitting device for thedisplay portion 7203.

FIG. 6C illustrates a portable game machine, which includes twohousings, i.e., a housing 7301 and a housing 7302, connected to eachother via a joint portion 7303 so that the portable game machine can beopened or closed. A display portion 7304 is incorporated in the housing7301 and a display portion 7305 is incorporated in the housing 7302. Inaddition, the portable game machine illustrated in FIG. 6C includes aspeaker portion 7306, a recording medium insertion portion 7307, an LEDlamp 7308, input means (an operation key 7309, a connection terminal7310, a sensor 7311 (a sensor having a function of measuring force,displacement, position, speed, acceleration, angular velocity,rotational frequency, distance, light, liquid, magnetism, temperature,chemical substance, sound, time, hardness, electric field, electriccurrent, voltage, electric power, radiation, flow rate, humidity,gradient, oscillation, odor, or infrared rays), and a microphone 7312),and the like. It is needless to say that the structure of the portablegame machine is not limited to the above structure as long as thelight-emitting device is used for at least either the display portion7304 or the display portion 7305, or both, and may include otheraccessories as appropriate. The portable game machine illustrated inFIG. 6C has a function of reading out a program or data stored in astorage medium to display it on the display portion, and a function ofsharing information with another portable game machine by wirelesscommunication. Note that a function of the portable game machineillustrated in FIG. 6C is not limited to the above, and the portablegame machine can have a variety of functions.

FIG. 6D illustrates an example of a cellular phone. A cellular phone7400 is provided with a display portion 7402 incorporated in a housing7401, operation buttons 7403, an external connection port 7404, aspeaker 7405, a microphone 7406, and the like. Note that the cellularphone 7400 is manufactured using the light-emitting device for thedisplay portion 7402.

When the display portion 7402 of the cellular phone 7400 illustrated inFIG. 6D is touched with a finger or the like, data can be input to thecellular phone 7400. Further, operations such as making a call andcreating e-mail can be performed by touch on the display portion 7402with a finger or the like.

There are mainly three screen modes for the display portion 7402. Thefirst mode is a display mode mainly for displaying an image. The secondmode is an input mode mainly for inputting information such ascharacters. The third mode is a display-and-input mode in which twomodes of the display mode and the input mode are mixed.

For example, in the case of making a call or creating e-mail, the inputmode mainly for inputting characters is selected for the display portion7402 so that characters displayed on the screen can be input. In thiscase, it is preferable to display a keyboard or number buttons on almostthe entire screen of the display portion 7402.

When a detection device including a sensor for detecting inclination,such as a gyroscope or an acceleration sensor, is provided inside thecellular phone 7400, display on the screen of the display portion 7402can be automatically changed by determining the orientation of thecellular phone 7400 (whether the cellular phone is placed horizontallyor vertically for a landscape mode or a portrait mode).

The screen modes are changed by touch on the display portion 7402 oroperation with the operation buttons 7403 of the housing 7401.Alternatively, the screen modes can be changed depending on the kind ofimage displayed on the display portion 7402. For example, when a signalfor an image to be displayed on the display portion is data of movingimages, the screen mode is changed to the display mode. When the signalis text data, the screen mode is changed to the input mode.

Moreover, in the input mode, if a signal detected by an optical sensorin the display portion 7402 is detected and the input by touch on thedisplay portion 7402 is not performed for a certain period, the screenmode may be controlled so as to be changed from the input mode to thedisplay mode.

The display portion 7402 may function as an image sensor. For example,an image of a palm print, a fingerprint, or the like is taken by touchon the display portion 7402 with the palm or the finger, wherebypersonal identification can be performed. Furthermore, when a backlightor a sensing light source which emits near-infrared light is providedfor the display portion, an image of a finger vein, a palm vein, or thelike can also be taken.

FIGS. 7A and 7B illustrate a foldable tablet terminal. The tabletterminal is opened in FIG. 7A. The tablet terminal includes a housing9630, a display portion 9631 a, a display portion 9631 b, a display modeswitch 9034, a power switch 9035, a power saver switch 9036, a clasp9033, and an operation switch 9038. The tablet terminal is manufacturedusing the light-emitting device for either the display portion 9631 a orthe display portion 9631 b or both.

Part of the display portion 9631 a can be a touch panel region 9632 aand data can be input when a displayed operation key 9637 is touched.Although a structure in which half of the display portion 9631 a hasonly a display function and the other half has a touch panel function isshown as an example, one embodiment of the present invention is notlimited to the structure. The whole region in the display portion 9631 amay have a touch panel function. For example, the display portion 9631 acan display keyboard buttons in the whole region to be a touch panel,and the display portion 9631 b can be used as a display screen.

In the display portion 9631 b, as in the display portion 9631 a, part ofthe display portion 9631 b can be a touch panel region 9632 b. When akeyboard display switching button 9639 displayed on the touch panel istouched with a finger, a stylus, or the like, keyboard buttons can bedisplayed on the display portion 9631 b.

Touch input can be performed in the touch panel region 9632 a and thetouch panel region 9632 b at the same time.

The display mode switch 9034 can switch the display between a portraitmode, a landscape mode, and the like, and between monochrome display andcolor display, for example. The power saver switch 9036 can controldisplay luminance in accordance with the amount of external light in useof the tablet terminal detected by an optical sensor incorporated in thetablet terminal. In addition to the optical sensor, another detectiondevice including a sensor for detecting inclination, such as a gyroscopeor an acceleration sensor, may be incorporated in the tablet terminal.

Although the display portion 9631 a and the display portion 9631 b havethe same display area in FIG. 7A, one embodiment of the presentinvention is not limited to this example. One of the display portionsmay be different from the other display portion in size and displayquality. For example, one of them may be a display panel that candisplay higher-definition images than the other.

The tablet terminal is closed in FIG. 7B. The tablet terminal includesthe housing 9630, a solar cell 9633, a charge and discharge controlcircuit 9634, a battery 9635, and a DCDC converter 9636. In FIG. 7B, astructure including the battery 9635 and the DCDC converter 9636 isillustrated as an example of the charge and discharge control circuit9634.

Since the tablet terminal is foldable, the housing 9630 can be closedwhen the tablet terminal is not used. As a result, the display portion9631 a and the display portion 9631 b can be protected; thus, a tabletterminal which has excellent durability and excellent reliability interms of long-term use can be provided.

In addition, the tablet terminal illustrated in FIGS. 7A and 7B can havea function of displaying a variety of kinds of data (e.g., a stillimage, a moving image, and a text image), a function of displaying acalendar, a date, the time, or the like on the display portion, atouch-input function of operating or editing the data displayed on thedisplay portion by touch input, a function of controlling processing bya variety of kinds of software (programs), and the like.

The solar cell 9633 provided on a surface of the tablet terminal cansupply power to the touch panel, the display portion, a video signalprocessing portion, or the like. Note that the solar cell 9633 can beprovided on one or both surfaces of the housing 9630 and the battery9635 can be charged efficiently. The use of a lithium ion battery as thebattery 9635 is advantageous in downsizing or the like.

The structure and the operation of the charge and discharge controlcircuit 9634 illustrated in FIG. 7B will be described with reference toa block diagram in FIG. 7C. The solar cell 9633, the battery 9635, theDCDC converter 9636, a converter 9638, switches SW1 to SW3, and adisplay portion 9631 are illustrated in FIG. 7C, and the battery 9635,the DCDC converter 9636, the converter 9638, and the switches SW1 to SW3correspond to the charge and discharge control circuit 9634 illustratedin FIG. 7B.

First, an example of the operation in the case where power is generatedby the solar cell 9633 using external light is described. The voltage ofpower generated by the solar cell 9633 is stepped up or down by the DCDCconverter 9636 so that the power has voltage for charging the battery9635. Then, when the power from the solar cell 9633 is used for theoperation of the display portion 9631, the switch SW1 is turned on andthe voltage of the power is stepped up or down by the converter 9638 soas to be voltage needed for the display portion 9631. In addition, whendisplay on the display portion 9631 is not performed, the switch SW1 isturned off and the switch SW2 is turned on so that the battery 9635 maybe charged.

Note that the solar cell 9633 is shown as an example of a powergeneration means; however, there is no particular limitation on a way ofcharging the battery 9635, and the battery 9635 may be charged usinganother power generation means such as a piezoelectric element or athermoelectric conversion element (Peltier element). For example, anon-contact electric power transmission module which transmits andreceives power wirelessly (without contact) to charge the battery 9635,or a combination of the solar cell 9633 and another means for charge maybe used.

It is needless to say that one embodiment of the present invention isnot limited to the electronic device illustrated in FIGS. 7A to 7C aslong as the display portion described in the above embodiment isincluded.

As described above, the electronic devices can be obtained by the use ofthe light-emitting device which is one embodiment of the presentinvention. The light-emitting device has a remarkably wide applicationrange, and can be applied to electronic devices in a variety of fields.

Note that the structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

Embodiment 7

In this embodiment, examples of lighting devices will be described withreference to FIG. 8. A light-emitting device including a light-emittingelement which is one embodiment of the present invention is applied tothe lighting devices.

FIG. 8 illustrates an example in which the light-emitting device is usedfor an interior lighting device 8001. Since the light-emitting devicecan have a larger area, a lighting device having a large area can alsobe formed. In addition, a lighting device 8002 in which a light-emittingregion has a curved surface can also be formed with the use of a housingwith a curved surface. A light-emitting element included in thelight-emitting device described in this embodiment is in the form of athin film, which allows the housing to be designed more freely. Thus,the lighting device can be elaborately designed in a variety of ways.Further, a wall of the room may be provided with a large-sized lightingdevice 8003.

Moreover, when the light-emitting device is used for a table by beingused as a surface of a table, a lighting device 8004 which has afunction as a table can be obtained. When the light-emitting device isused as part of other furniture, a lighting device which has a functionas the furniture can be obtained.

In this manner, a variety of lighting devices to which thelight-emitting device is applied can be obtained. Note that suchlighting devices are also embodiments of the present invention.

The structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

Example 1 Synthesis Example 1

In this example, a method for synthesizing4-[3′-(4-dibenzothienyl)-1,1′-biphenyl-3-yl]-2,6-diphenylpyrimidine(abbreviation: 2,6Ph-4mDBTBPPm-II), which is the heterocyclic compoundof one embodiment of the present invention represented by StructuralFormula (100) in Embodiment 1, will be described. A structure of2,6Ph-4mDBTBPPm-II (abbreviation) is shown below.

Step 1: Synthesis of 4-(3-Bromophenyl)-2,6-diphenylpyrimidine

Synthesis Scheme (B-1) of 4-(3-bromophenyl)-2,6-diphenylpyrimidine isshown below.

Into a 500-mL three-neck flask were put 18.5 g (100.0 mmol) of3-bromobenzaldehyde and 12.0 g (100.0 mmol) of acetophenone, the air inthe flask was replaced with nitrogen, and 100 mL of ethanol was added.To this mixture, 6.0 g (111.0 mmol) of sodium methoxide suspended in 100mL of ethanol was added dropwise, and the mixture was stirred at roomtemperature for 22 hours. After the stirring for the predetermined time,15.6 g (100.0 mmol) of benzamidine hydrochloride and 8.0 g (200.0 mmol)of sodium hydroxide were added and the mixture was stirred at 70° C. for3 hours. After the stirring, the mixture was filtered. Water was addedto the residue and ultrasonic cleaning was performed. A solid wascollected by suction filtration, so that 14.4 g of a white solid wasobtained in a yield of 38.0%.

Step 2: Synthesis of 2,6Ph-4mDBTBPPm-II (abbreviation)

Synthesis Scheme (B-2) of 2,6Ph-4mDBTBPPm-II (abbreviation) is shownbelow.

Into a 500-mL three-neck flask were put 7.75 g (20.0 mmol) of4-(3-bromophenyl)-2,6-diphenylpyrimidine, 7.60 g (25.0 mmol) of3-(dibenzothiophen-4-yl)phenylboronic acid, and 608.7 mg (2.0 mmol) oftris(o-tolyl)phosphine. To this mixture, 155 mL of toluene, 20 mL ofethanol, and 25 mL of a 2M aqueous solution of potassium carbonate wereadded. After this mixture was degassed while being stirred under areduced pressure, 224.5 mg (1.0 mmol) of palladium(II) acetate wasadded. The mixture was heated and stirred at 80° C. under a nitrogenstream for 2.5 hours to cause a reaction. After the reaction, 1300 mL oftoluene was added and an organic layer and an aqueous layer wereseparated. The aqueous layer was subjected to extraction with toluene.The solution of the extract and the organic layer were combined, washedwith a saturated aqueous solution of sodium chloride, and dried overmagnesium sulfate. After the drying, the mixture was subjected togravity filtration. Then, filtration through Celite and alumina wasperformed, and the filtrate was concentrated. Recrystallization withtoluene was performed to give 9.64 g of a white solid in a yield of85.1%.

Results of analysis by nuclear magnetic resonance (¹H-NMR) spectroscopyof the compound obtained by the above-described synthesis method aredescribed below. The ¹H-NMR charts are shown in FIGS. 9A and 9B. Theresults reveal that 2,6Ph-4mDBTBPPm-II (abbreviation), which is theheterocyclic compound of one embodiment of the present inventionrepresented by Structural Formula (100), was obtained.

¹H NMR (CDCl₃, 500 MHz): δ=7.46-7.61 (m, 10H), 7.66-7.70 (dt, J=2.5 Hz,7.8 Hz, 2H), 7.78-7.81 (t, J=7.7 Hz, 3H), 7.87-7.88 (d, J=8.0 Hz, 1H),8.01 (s, 1H), 8.14-8.15 (t, J=1.7 Hz, 1H), 8.20-8.23 (m, 2H), 8.31-8.33(dd, J=2.3 Hz, 7.4 Hz, 3H), 8.60-8.61 (t, J=1.7 Hz, 1H), 8.74-8.63 (m,2H).

Next, 2,6Ph-4mDBTBPPm-II (abbreviation) obtained in this example wasanalyzed by liquid chromatography mass spectrometry (LC/MS).

The analysis by LC/MS was carried out with Acquity UPLC (produced byWaters Corporation) and Xevo G2 T of MS (produced by WatersCorporation).

In the MS analysis, ionization was carried out by an electrosprayionization (ESI) method. Capillary voltage and sample cone voltage wereset to 3.0 kV and 30 V, respectively. Detection was performed in apositive mode. A component which underwent the ionization under theabove-mentioned conditions was collided with an argon gas in a collisioncell to dissociate into product ions. Energy (collision energy) for thecollision with argon was 70 eV. A mass range for the measurement wasm/z=100-1200.

FIG. 10 shows the measurement results. The results in FIG. 10 show thatas for 2,6Ph-4mDBTBPPm-II (abbreviation), which is the heterocycliccompound of one embodiment of the present invention represented byStructural Formula (100), product ions are detected mainly aroundm/z=361, m/z=345, m/z=258, m/z=128, and m/z=104. Note that the resultsin FIG. 10 show characteristics derived from 2,6Ph-4mDBTBPPm-II(abbreviation) and therefore can be regarded as important data foridentifying 2,6Ph-4mDBTBPPm-II (abbreviation) contained in a mixture.

It is probable that a C—C bond next to the nitrogen atom of thepyrimidine ring is cut, electric charge remains in a fragment containingthe nitrogen atom, and the data appearing around m/z=361, m/z=128, andm/z=104 is thus data on a state where the C—C bond next to the nitrogenatom of the pyrimidine ring of the compound represented by StructuralFormula (100) is cut; accordingly, the data is useful. In addition, theproduct ion around m/z=345 can be presumed to be a product ion includingone dibenzothiophene ring and two benzene rings, and the product ionaround m/z=258 can be presumed to be a product ion including onedibenzothiophene ring and one benzene ring; thus, it is suggested that2,6Ph-4mDBTBPPm-II (abbreviation), which is the heterocyclic compound ofone embodiment of the present invention, includes a dibenzothiophenering.

Example 2 Synthesis Example 2

In this example, a method for synthesizing4-[3′-(4-dibenzothienyl)-1,1′-biphenyl-4-yl]-2,6-diphenylpyrimidine(abbreviation: 2,6Ph-4pmDBTBPPm-II), which is the heterocyclic compoundof one embodiment of the present invention represented by StructuralFormula (101) in Embodiment 1, will be described. A structure of2,6Ph-4pmDBTBPPm-II (abbreviation) is shown below.

Step 1: Synthesis of 4-(4-Bromophenyl)-2,6-diphenylpyrimidine

Synthesis Scheme (C-1) of 4-(4-bromophenyl)-2,6-diphenylpyrimidine isshown below.

Into a 300-mL three-neck flask were put 11 mL (94.6 mmol) ofacetophenone and 17.9 g (96.7 mmol) of 4-bromobenzaldehyde, and the airin the flask was replaced with nitrogen. To this mixture, 50 mL ofethanol was added and 5.99 g (110.9 mmol) of sodium methoxide suspendedin 50 mL of ethanol was added dropwise. The mixture was stirred at roomtemperature for 5 hours and further stirred at 70° C. for 50 minutes.After the predetermined time elapsed, 15.1 g (96.6 mmol) of benzamidinehydrochloride and 8.03 g (200 mmol) of sodium hydroxide were added andthe mixture was stirred at 70° C. for 9 hours. After the predeterminedtime elapsed, this mixture was suction-filtered, and the obtainedresidue was dissolved in chloroform and subjected to extraction withwater. The obtained organic layer was washed with a saturated aqueoussolution of sodium chloride and dried over magnesium sulfate. Thismixture was subjected to gravity filtration, and the solvent wasdistilled off to give a solid. The obtained solid was washed withethanol, so that 8.61 g of an objective white solid was obtained in ayield of 22%.

In addition, the filtrate obtained after the suction filtration wasconcentrated, followed by purification using silica gel columnchromatography. Toluene was used as a developing solvent. The obtainedfraction was concentrated and recrystallization with ethanol wasperformed. The obtained solid was subjected to ultrasonic cleaning usingethanol, so that 1.03 g of the objective white solid was obtained in ayield of 2.7%.

Step 2: Synthesis of 2,6Ph-4pmDBTBPPm-II (abbreviation)

Synthesis Scheme (C-2) of 2,6Ph-4pmDBTBPPm-II (abbreviation) is shownbelow.

Into a 200-mL three-neck flask were put 5.03 g (13.0 mmol) of4-(4-bromophenyl)-2,6-diphenylpyrimidine, 5.10 g (16.8 mmol) of3-(dibenzothiophen-4-yl)phenylboronic acid, 0.15 g (0.49 mmol) oftris(2-methylphenyl)phosphine, 50 mL of toluene, 16 mL of ethanol, and16 mL of a 2M aqueous solution of potassium carbonate. This mixture wasdegassed by being stirred while the pressure was reduced, and after thedegasification, 64 mg (0.29 mmol) of palladium acetate was added. Themixture was stirred at 90° C. under a nitrogen stream for 3 hours. Afterthe predetermined time elapsed, this mixture was subjected to suctionfiltration. Water was added to the obtained filtrate, and the aqueouslayer was subjected to extraction with toluene. The solution of theextract combined with the organic layer was washed with water and asaturated aqueous solution of sodium chloride and dried over magnesiumsulfate. The mixture was subjected to gravity filtration. The obtainedfiltrate was concentrated and combined with the residue collected afterthe suction filtration, and was dissolved in hot toluene. The mixturewas suction-filtered through Celite, alumina, and Florisil. The obtainedmixture was concentrated and subjected to ultrasonic cleaning usingethanol and recrystallization using toluene; thus, 4.66 g of theobjective white solid was obtained in a yield of 63%.

Then, 3.83 g of the obtained white solid was purified by sublimationusing a train sublimation method. In the purification by sublimation,the white solid was heated at 280° C. under a pressure of 2.7 Pa with aflow rate of argon of 5 mL/min After the purification by sublimation,3.39 g of a white solid was obtained at a collection rate of 88.6%.

Results of analysis by nuclear magnetic resonance (¹H-NMR) spectroscopyof the compound obtained by the above-described synthesis method aredescribed below. The ¹H-NMR charts are shown in FIGS. 11A and 11B. Theresults reveal that 2,6Ph-4pmDBTBPPm-II (abbreviation), which is theheterocyclic compound of one embodiment of the present inventionrepresented by Structural Formula (101), was obtained.

¹H NMR (CDCl₃, 500 MHz): δ=7.49-7.68 (m, 10H), 7.78 (dd, J=7.5 Hz, 2.0Hz, 2H), 7.86-7.88 (m, 1H), 7.91 (d, J=8.5 Hz, 2H), 8.09 (s, 1H), 8.11(t, J=1.7 Hz, 1H), 8.22 (m, 2H), 8.32 (dd, J=8.0 Hz, 2.0 Hz, 2H), 8.43(d, J=8.5 Hz, 2H), 8.76 (dd, J=8.0 Hz, 2.0 Hz, 2H).

Next, 2,6Ph-4pmDBTBPPm-II (abbreviation) obtained in this example wasanalyzed by liquid chromatography mass spectrometry (LC/MS).

The analysis by LC/MS was carried out with Acquity UPLC (produced byWaters Corporation) and Xevo G2 T of MS (produced by WatersCorporation).

In the MS analysis, ionization was carried out by an electrosprayionization (ESI) method. Capillary voltage and sample cone voltage wereset to 3.0 kV and 30 V, respectively. Detection was performed in apositive mode. A component which underwent the ionization under theabove-mentioned conditions was collided with an argon gas in a collisioncell to dissociate into product ions. Energy (collision energy) for thecollision with argon was 70 eV. A mass range for the measurement wasm/z=100-1200.

FIG. 12 shows the measurement results. The results in FIG. 12 show thatas for 2,6Ph-4pmDBTBPPm-II (abbreviation), which is the heterocycliccompound of one embodiment of the present invention represented byStructural Formula (101), product ions are detected mainly aroundm/z=361, m/z=345, m/z=258, m/z=128, and m/z=104. Note that the resultsin FIG. 12 show characteristics derived from 2,6Ph-4pmDBTBPPm-II(abbreviation) and therefore can be regarded as important data foridentifying 2,6Ph-4pmDBTBPPm-II (abbreviation) contained in a mixture.

It is probable that a C—C bond next to the nitrogen atom of thepyrimidine ring is cut, electric charge remains in a fragment containingthe nitrogen atom, and the data appearing around m/z=361, m/z=128, andm/z=104 is thus data on a state where the C—C bond next to the nitrogenatom of the pyrimidine ring of the compound represented by StructuralFormula (100) is cut; accordingly, the data is useful. In addition, theproduct ion around m/z=345 can be presumed to be a product ion includingone dibenzothiophene ring and two benzene rings, and the product ionaround m/z=258 can be presumed to be a product ion including onedibenzothiophene ring and one benzene ring; thus, it is suggested that2,6Ph-4pmDBTBPPm-II (abbreviation), which is the heterocyclic compoundof one embodiment of the present invention, includes a dibenzothiophenering.

Example 3

In this example, a light-emitting element 1 and a light-emitting element2 each including a heterocyclic compound of one embodiment of thepresent invention in part of a light-emitting layer and anelectron-transport layer will be described with reference to FIG. 13.The heterocyclic compounds included in the light-emitting element 1 andthe light-emitting element 2 are4-[3′-(4-dibenzothienyl)-1,1′-biphenyl-3-yl]-2,6-diphenylpyrimidine(abbreviation: 2,6Ph-4-mDBTBPPm-II) represented by Structural Formula(100) and4-[3′-(4-dibenzothienyl)-1,1′-biphenyl-4-yl]-2,6-diphenylpyrimidine(abbreviation: 2,6Ph-4pmDBTBPPm-II) represented by Structural Formula(101), respectively. Chemical formulae of materials used in this exampleare shown below.

<<Fabrication of Light-Emitting Element 1 and Light-Emitting Element 2>>

First, indium tin oxide containing silicon oxide (ITSO) was depositedover a glass substrate 1100 by a sputtering method, so that a firstelectrode 1101 which functions as an anode was formed. The thickness was110 nm and the electrode area was 2 mm×2 mm.

Next, as pretreatment for forming the light-emitting element over thesubstrate 1100, the surface of the substrate was washed with water,baked at 200° C. for 1 hour, and subjected to UV ozone treatment for 370seconds.

After that, the substrate 1100 was transferred into a vacuum evaporationapparatus where the pressure had been reduced to approximately 10⁻⁴ Pa,and subjected to vacuum baking at 170° C. for 30 minutes in a heatingchamber of the vacuum evaporation apparatus, and then the substrate 1100was cooled down for about 30 minutes.

Next, the substrate 1100 was fixed to a holder provided in the vacuumevaporation apparatus so that a surface of the substrate 1100 over whichthe first electrode 1101 was formed faced downward. In this example, acase is described in which a hole-injection layer 1111, a hole-transportlayer 1112, a light-emitting layer 1113, an electron-transport layer1114, and an electron-injection layer 1115 which are included in an ELlayer 1102 are sequentially formed by a vacuum evaporation method.

After reducing the pressure of the vacuum evaporation apparatus to 10⁻⁴Pa, 1,3,5-tri(dibenzothiophen-4-yl)benzene (abbreviation: DBT3P-II) andmolybdenum(VI) oxide were deposited by co-evaporation with a mass ratioof 4:2 (=DBT3P-II (abbreviation): molybdenum oxide), so that thehole-injection layer 1111 was formed over the first electrode 1101. Thethickness of the hole-injection layer 1111 was 40 nm. Note thatco-evaporation is an evaporation method in which a plurality ofdifferent substances are concurrently vaporized from respectivedifferent evaporation sources.

Then, 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation:BPAFLP) and 3,3′-bis(9-phenyl-9H-carbazole) (abbreviation: PCCP) weredeposited by co-evaporation with a mass ratio of BPAFLP (abbreviation)to PCCP (abbreviation) being 1:1, whereby the hole-transport layer 1112was formed. The thickness was 20 nm.

Next, the light-emitting layer 1113 was formed over the hole-transportlayer 1112.

In the light-emitting element 1, the light-emitting layer 1113 with astacked-layer structure was formed to have a thickness of 40 nm bydepositing 2,6Ph-4mDBTBPPm-II (abbreviation),4,4′-di(1-naphthyl)-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBNBB), and(acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III)(abbreviation: [Ir(tBuppm)₂(acac)]) by co-evaporation to a thickness of20 nm with a mass ratio of 2,6Ph-4mDBTBPPm-II (abbreviation) to PCBNBB(abbreviation) and [Ir(tBuppm)₂(acac)] (abbreviation) being0.5:0.5:0.05, and then depositing 2,6Ph-4mDBTBPPm-II (abbreviation),PCBNBB (abbreviation), and [Ir(tBuppm)₂(acac)] (abbreviation) to athickness of 20 nm with a mass ratio of 2,6Ph-4mDBTBPPm-II(abbreviation) to PCBNBB (abbreviation) and [Ir(tBuppm)₂(acac)](abbreviation) being 0.8:0.2:0.05.

In the light-emitting element 2, the light-emitting layer 1113 with astacked-layer structure was formed to have a thickness of 40 nm bydepositing 2,6Ph-4pmDBTBPPm-II (abbreviation), PCBNBB (abbreviation),and [Ir(tBuppm)₂(acac)] (abbreviation) by co-evaporation to a thicknessof 20 nm with a mass ratio of 2,6Ph-4pmDBTBPPm-II (abbreviation) toPCBNBB (abbreviation) and [Ir(tBuppm)₂(acac)] (abbreviation) being0.5:0.5:0.05, and then depositing 2,6Ph-4pmDBTBPPm-II (abbreviation),PCBNBB (abbreviation), and [Ir(tBuppm)₂(acac)] (abbreviation) to athickness of 20 nm with a mass ratio of 2,6Ph-4pmDBTBPPm-II(abbreviation) to PCBNBB (abbreviation) and [Ir(tBuppm)₂(acac)](abbreviation) being 0.8:0.2:0.05.

Note that in each of the light-emitting element 1 and the light-emittingelement 2 in this example, exciplex formation in the light-emittinglayer is possible.

Then, in the light-emitting element 1, 2,6Ph-4-mDBTBPPm-II(abbreviation) was deposited by evaporation to a thickness of 10 nm overthe light-emitting layer 1113 and bathophenanthroline (abbreviation:Bphen) was then deposited by evaporation to a thickness of 20 nm,whereby the electron-transport layer 1114 having a stacked-layerstructure was formed. In the light-emitting element 2,2,6Ph-4pmDBTBPPm-II (abbreviation) was deposited by evaporation to athickness of 10 nm over the light-emitting layer 1113 andbathophenanthroline (abbreviation: Bphen) was then deposited byevaporation to a thickness of 20 nm, whereby the electron-transportlayer 1114 having a stacked-layer structure was formed.

Furthermore, lithium fluoride was deposited by evaporation to athickness of 1 nm over the electron-transport layer 1114, whereby theelectron-injection layer 1115 was formed.

Finally, aluminum was deposited by evaporation to a thickness of 200 nmover the electron-injection layer 1115 to form a second electrode 1103serving as a cathode; thus, the light-emitting element 1 and thelight-emitting element 2 were obtained. Note that in all the aboveevaporation steps, evaporation was performed by a resistance heatingmethod.

Table 1 shows element structures of the light-emitting element 1 and thelight-emitting element 2 obtained through the above-described steps.

TABLE 1 Hole- Light- Electron- First Hole-injection transport emittinginjection Second electrode Layer Layer Layer Electron-transport LayerLayer Electrode Light- ITSO DBT3P-II: BPAFLP: * ** 2,6Ph-4mDBTBPPm-IIBphen LiF Al emitting (110 nm) MoO_(x) PCCP (10 nm) (20 nm) (1 nm) (200nm) Element 1 (4:2 40 nm) (1:1 20 nm) Light- ITSO DBT3P-II: BPAFLP: ******* 2,6Ph-4pmDBTBPPm-II Bphen LiF Al emitting (110 nm) MoO_(x) PCCP (10nm) (20 nm) (1 nm) (200 nm) Element 2 (4:2 40 nm) (1:1 20 nm) *2,6Ph-4mDBTBPPm-II:PCBNBB:[Ir(tBuppm)₂(acac)] (0.5:0.5:0.05 20 nm) **2,6Ph-4mDBTBPPm-II:PCBNBB:[Ir(tBuppm)₂(acac)] (0.8:0.2:0.05 20 nm) ***2,6Ph-4pmDBTBPPm-II:PCBNBB:[Ir(tBuppm)₂(acac)] (0.5:0.5:0.05 20 nm) ****2,6Ph-4pmDBTBPPm-II:PCBNBB:[Ir(tBuppm)₂(acac)] (0.8:0.2:0.05 20 nm)

Further, the fabricated light-emitting elements 1 and 2 were sealed in aglove box containing a nitrogen atmosphere so as not to be exposed tothe air (specifically, a sealant was applied onto an outer edge of theelement and heat treatment was performed at 80° C. for 1 hour at thetime of sealing).

<<Operation Characteristics of Light-Emitting Element 1 andLight-Emitting Element 2>>

Operation characteristics of the fabricated light-emitting elements 1and 2 were measured. Note that the measurement was carried out at roomtemperature (in an atmosphere kept at 25° C.).

FIG. 14 shows current density-luminance characteristics of thelight-emitting elements 1 and 2, FIG. 15 shows voltage-luminancecharacteristics thereof, FIG. 16 shows luminance-current efficiencycharacteristics thereof, and FIG. 17 shows voltage-currentcharacteristics thereof.

FIG. 16 reveals that the light-emitting element 1 and the light-emittingelement 2, which use the heterocyclic compounds of embodiments of thepresent invention in the light-emitting layers and theelectron-transport layers, have reduced power consumption and highefficiency.

Table 2 shows initial values of main characteristics of thelight-emitting elements 1 and 2 at a luminance of about 1000 cd/m².

TABLE 2 External Current Current Power Quantum Voltage Current DensityChromaticity Luminance Efficiency Efficiency Efficiency (V) (mA)(mA/cm²) (x, y) (cd/m²) (cd/A) (lm/W) (%) Light- 3.1 0.067 1.7 (0.42,0.56) 1100 66 67 18 emitting Element 1 Light- 2.9 0.064 1.6 (0.41, 0.57)750 46 50 13 emitting Element 2

The above results in Table 2 also show that the light-emitting elements1 and 2 fabricated in this example have high luminance and high currentefficiency.

The light-emitting elements 1 and 2 were subjected to reliability tests.FIG. 18 shows results of the reliability tests. In FIG. 18, the verticalaxis indicates normalized luminance (%) with an initial luminance of100% and the horizontal axis indicates driving time (h) of the element.Note that in the reliability tests, the light-emitting elements 1 and 2were driven under the conditions where the initial luminance was set to5000 cd/m² and the current density was constant. The light-emittingelements 1 and 2 kept about 83% of the initial luminance after 100 hourselapsed.

The results of the reliability tests showed that the light-emittingelement 1 and the light-emitting element 2 have high reliability. Inaddition, it was confirmed that with the use of the heterocycliccompound that is one embodiment of the present invention, alight-emitting element with a long lifetime can be obtained.

Example 4 Synthesis Example 3

In this example, a method for synthesizing4-[3′-(dibenzothiophen-4-yl)-1,1′-biphenyl-3-yl]-6-phenylpyrimidine(abbreviation: 6Ph-4mDBTBPPm-II), which is the heterocyclic compound ofone embodiment of the present invention represented by StructuralFormula (112) in Embodiment 1, will be described. A structure of6Ph-4mDBTBPPm-II (abbreviation) is shown below.

Step 1: Synthesis of 4-Chloro-6-phenylpyrimidine

Into a 100-mL round-bottom flask equipped with a reflux pipe were put5.1 g of 4,6-dichloropyrimidine, 8.2 g of phenylboronic acid, 7.16 g ofsodium carbonate, 20 mL of acetonitrile, and 20 mL of water, and the airin the flask was replaced with nitrogen. To this mixture, 0.347 g ofbis(triphenylphosphine)palladium(II) dichloride was added and themixture was irradiated with microwaves (2.45 GHz, 100 W) for 1 hour.Further, 2.07 g of phenylboronic acid and 1.79 g of sodium carbonatewere added and the mixture was irradiated with microwaves (2.45 GHz, 100W) for 1 hour. An organic layer was extracted from the obtained mixturewith the use of dichloromethane. The obtained organic layer was washedwith water and a saturated aqueous solution of sodium chloride and driedover magnesium sulfate. The mixture was subjected to gravity filtration.A residue obtained by distilling off the solvent in the filtrate waspurified by silica column chromatography with the use of dichloromethaneas a developing solvent to give an objective substance as a white powderin a yield of 37%. Note that the irradiation with microwaves wasperformed using a microwave synthesis system (Discover, manufactured byCEM Corporation). Synthesis Scheme (D-1) of Step 1 is shown below.

Step 2: Synthesis of4-[3′-(Dibenzothiophen-4-yl)-1,1′-biphenyl-3-yl]-6-phenylpyrimidine(abbreviation: 6Ph-4mDBTBPPm-II)

Then, 1.0 g of 4-chloro-6-phenylpyrimidine obtained in Step 1, 2.0 g of3′-(dibenzothiophen-4-yl)-3-biphenylboronic acid, 5.3 mL of a 2M aqueoussolution of potassium carbonate, 24 mL of toluene, and 3.0 mL of ethanolwere put into a 100-mL three-neck flask equipped with a reflux pipe.Degasification by stirring under a reduced pressure was performed andthe air in the flask was replaced with nitrogen. To this mixture, 61 mgof tetrakis(triphenylphosphine)palladium(0) (abbreviation: Pd(PPh₃)₄)was added and the mixture was heated at 80° C. for 7 hours to cause areaction. An organic layer was extracted from the obtained mixture withthe use of toluene and was washed with water and a saturated aqueoussolution of sodium chloride. Anhydrous magnesium sulfate was added andgravity filtration was performed. After the solvent in this solution wasdistilled off, the obtained residue was dissolved in hot toluene andsubjected to hot filtration through a filter aid in which Celite,alumina, Celite, Florisil, and Celite were stacked in this order. Thesolvent was distilled off and the obtained solid was recrystallized withtoluene, so that 1.9 g of a white solid was obtained in a yield of 71%.Synthesis Scheme (D-2) of Step 2 is shown below.

Then, 2.4 g of the obtained solid was purified by sublimation using atrain sublimation method. Conditions for the purification by sublimationwere set as follows: the pressure was 3.0 Pa, the flow rate of argon gaswas 15 mL/min, and the heating temperature was 265° C. After thepurification by sublimation, 1.9 g of colorless transparent crystals ofthe objective substance were obtained at a collection rate of 79%.

Results of analysis by nuclear magnetic resonance (¹H-NMR) spectroscopyof the white solid obtained in Step 2 are described below. The ¹H-NMRchart is shown in FIG. 19. The results reveal that 6Ph-4mDBTBPPm-II(abbreviation), which is the heterocyclic compound of one embodiment ofthe present invention represented by Structural Formula (112), wasobtained.

¹H-NMR. δ(CDCl₃): 7.45-7.50 (dm, 2H), 7.52-7.54 (m, 3H), 7.56-7.61 (m,2H), 7.63-7.67 (m, 2H), 7.76-7.77 (ds, 1H), 7.78 (ds, 1H), 7.82-7.83(dd, 1H), 7.85-7.87 (dd, 1H), 8.08-8.09 (ts, 1H), 8.14-8.22 (dm, 6H),8.45-8.46 (ts, 1H), 9.34-9.35 (ds, 1H).

Next, 6Ph-4mDBTBPPm-II (abbreviation) was analyzed by liquidchromatography mass spectrometry (LC/MS).

The analysis by LC/MS was carried out with Acquity UPLC (produced byWaters Corporation) and Xevo G2 T of MS (produced by WatersCorporation).

In the MS analysis, ionization was carried out by an electrosprayionization (ESI) method. Capillary voltage and sample cone voltage wereset to 3.0 kV and 30 V, respectively. Detection was performed in apositive mode. A component which underwent the ionization under theabove-mentioned conditions was collided with an argon gas in a collisioncell to dissociate into product ions. Energy (collision energy) for thecollision with argon was 50 eV and 70 eV. A mass range for themeasurement was m/z=100-1200.

FIG. 20 and FIG. 21 show the measurement results. FIG. 20 shows theresults at the time when the collision energy was 50 eV. FIG. 21 showsthe results at the time when the collision energy was 70 eV. The resultsin FIG. 20 and FIG. 21 show that as for 6Ph-4mDBTBPPm-II (abbreviation),which is the heterocyclic compound of one embodiment of the presentinvention represented by Structural Formula (112), product ions aredetected mainly around m/z=447, m/z=361, m/z=345, m/z=258, m/z=128, andm/z=104. Note that the results in FIG. 20 and FIG. 21 showcharacteristics derived from 6Ph-4mDBTBPPm-II (abbreviation) andtherefore can be regarded as important data for identifying6Ph-4mDBTBPPm-II (abbreviation) contained in a mixture.

It is probable that a C—C bond next to the nitrogen atom of thepyrimidine ring is cut, electric charge remains in a fragment containingthe nitrogen atom, and the data appearing around m/z=361, m/z=128, andm/z=104 is thus data on a state where the C—C bond next to the nitrogenatom of the pyrimidine ring of the compound represented by StructuralFormula (112) is cut; accordingly, the data is useful. In addition, theproduct ion around m/z=345 can be presumed to be a product ion includingone dibenzothiophene ring and two benzene rings, and the product ionaround m/z=258 can be presumed to be a product ion including onedibenzothiophene ring and one benzene ring; thus, it is suggested that6Ph-4mDBTBPPm-II (abbreviation), which is the heterocyclic compound ofone embodiment of the present invention, includes a dibenzothiophenering.

Example 5 Synthesis Example 4

In this example, a method for synthesizing4-[3′-(dibenzothiophen-4-yl)-1,1′-biphenyl-3-yl]-6-(9,9-dimethylfluoren-2-yl)pyrimidine (abbreviation: 6FL-4mDBTBPPm), which is one embodiment of the presentinvention represented by Structural Formula (121) in Embodiment 1, willbe described. A structure of 6FL-4mDBTBPPm (abbreviation) is shownbelow.

Step 1: Synthesis of4-Chloro-6-[3-(3′-dibenzothiophen-4-yl)biphenyl]pyrimidine

First, 0.20 g (1.3 mmol) of 4,6-dichloropyrimidine, 0.51 g (1.3 mmol) of3′-(dibenzothiophen-4-yl)-3-biphenylboronic acid, 0.85 g (2.6 mmol) ofcesium carbonate, 0.2 mL (0.83 mmol) of tricyclohexylphosphine (Cy₃P),18 mg (0.020 mmol) of tris(dibenzylideneacetone)palladium(0)(Pd₂(dba)₃), and 10 mL of dioxane were put into a 100-mL round-bottomflask, the mixture was bubbled with argon for 15 minutes and irradiatedwith microwaves (85° C., 150 W) for 2 hours. An aqueous layer of theobtained solution was extracted with dichloromethane. The obtainedsolution of the extract and the organic layer were combined and washedwith water and a saturated aqueous solution of sodium chloride, andanhydrous magnesium sulfate was added to the organic layer for drying.This mixture was subjected to gravity filtration, and the filtrate wasconcentrated to give a solid. This solid was purified by flash columnchromatography using dichloromethane as a developing solvent.Purification by silica gel column chromatography using toluene as adeveloping solvent was further performed. A solid obtained byconcentration of the obtained fraction was recrystallized with toluene,so that 4-chloro-6-[3-(3′-dibenzothiophen-4-yl)biphenyl]pyrimidine wasobtained as a white solid in a yield of 44%. Synthesis Scheme (E-1) ofStep 1 is shown below.

Step 2: Synthesis of4-[3′-(Dibenzothiophen-4-yl)-1,1′-biphenyl-3-yl]-6-(9,9-dimethylfluoren-2-yl)pyrimidine (abbreviation: 6FL-4mDBTBPPm)

Then, 1.0 g (2.6 mmol) of4-chloro-6-[3-(3′-dibenzothiophen-4-yl)biphenyl]pyrimidine, 1.0 g (3.2mmol) of 9,9-dimethylfluorene-2-boronic acid pinacol ester, 15 mL oftoluene, 3 mL of ethanol, and 2.6 mL of a 2M aqueous solution ofpotassium carbonate were put into a 200-mL reaction container, and theair in the container was replaced with nitrogen. To this mixture, 30 mg(0.02 mmol) of tetrakis(triphenylphosphine)palladium(0) (Pd(PPh₃)₄) wasadded and the mixture was heated and stirred at 80° C. for 8 hours. Theaqueous layer of the obtained reacted solution was subjected toextraction with toluene, and the obtained solution of the extract andthe organic layer were combined and washed with water and a saturatedaqueous solution of sodium chloride. Anhydrous magnesium sulfate wasadded to the organic layer for drying, and the resulting mixture wassubjected to gravity filtration to give a filtrate. A solid which wasobtained by concentration of this filtrate was purified by silica gelcolumn chromatography. Toluene was used as a developing solvent. Theobtained fraction was concentrated to give a solid. This solid wasrecrystallized with ethanol, so that 6FL-4mDBTBPPm was obtained as awhite solid in a yield of 51%. Synthesis Scheme (E-2) of Step 2 is shownbelow.

Then, 0.81 g of the obtained solid was purified by sublimation using atrain sublimation method. Conditions for the purification by sublimationwere set as follows: the pressure was 2.6 Pa, the flow rate of argon gaswas 10 mL/min, and the heating temperature was 270° C. After thepurification by sublimation, 0.47 g of pale yellow transparent crystalsof the objective substance were obtained at a collection rate of 58%.

Results of analysis by nuclear magnetic resonance (¹H-NMR) spectroscopyof the white solid obtained in Step 2 are described below. The ¹H-NMRchart is shown in FIG. 22. The results reveal that 6FL-4mDBTBPPm(abbreviation), which is the heterocyclic compound of one embodiment ofthe present invention represented by Structural Formula (121), wasobtained in Synthesis Example 4.

¹H-NMR. δ(CDCl₃): 1.58 (s, 6H), 7.36-7.39 (m, 2H), 7.43-7.50 (m, 3H),7.57-7.61 (m, 2H), 7.77-7.80 (m, m), 7.85 (dd, 2H), 7.88 (d, 1H), 8.11(t, 1H), 8.14 (dd, 1H), 8.17-8.23 (m, 4H), 8.29 (d, 1H), 8.49 (t, 1H),9.37 (d, 1H).

Next, 6FL-4mDBTBPPm (abbreviation) was analyzed by liquid chromatographymass spectrometry (LC/MS).

The analysis by LC/MS was carried out with Acquity UPLC (produced byWaters Corporation) and Xevo G2 T of MS (produced by WatersCorporation).

In the MS analysis, ionization was carried out by an electrosprayionization (ESI) method. Capillary voltage and sample cone voltage wereset to 3.0 kV and 30 V, respectively. Detection was performed in apositive mode. A component which underwent the ionization under theabove-mentioned conditions was collided with an argon gas in a collisioncell to dissociate into product ions. Energy (collision energy) for thecollision with argon was 70 eV. A mass range for the measurement wasm/z=100-1200.

FIG. 23 shows the measurement results. The results in FIG. 23 show thatas for 6FL-4mDBTBPPm (abbreviation), which is the heterocyclic compoundof one embodiment of the present invention represented by StructuralFormula (121), product ions are detected mainly around m/z=591, m/z=547,m/z=362, m/z=345, and m/z=203. Note that the results in FIG. 23 showcharacteristics derived from 6FL-4mDBTBPPm (abbreviation) and thereforecan be regarded as important data for identifying 6FL-4mDBTBPPm(abbreviation) contained in a mixture.

It is probable that a C—C bond next to the nitrogen atom of thepyrimidine ring is cut, electric charge remains in a fragment containingthe nitrogen atom, and the data appearing around m/z=362 is thus data ona state where the C—C bond next to the nitrogen atom of the pyrimidinering of the compound represented by Structural Formula (121) is cut;accordingly, the data is useful. In addition, the product ion aroundm/z=345 can be presumed to be a product ion including onedibenzothiophene ring and two benzene rings; thus, it is suggested that6FL-4mDBTBPPm (abbreviation), which is the heterocyclic compound of oneembodiment of the present invention, includes a dibenzothiophene ring.

Example 6

In this example, a light-emitting element 3 and a light-emitting element4 each including a heterocyclic compound of one embodiment of thepresent invention in part of a light-emitting layer and anelectron-transport layer will be similarly described with reference toFIG. 13 used in Example 3. The heterocyclic compounds included in thelight-emitting element 3 and the light-emitting element 4 are4-[3′-(dibenzothiophen-4-yl)-1,1′-biphenyl-3-yl]-6-phenylpyrimidine(abbreviation: 6Ph-4mDBTBPPm-II) represented by Structural Formula (112)and4-[3′-(dibenzothiophen-4-yl)-1,1′-biphenyl-3-yl]-6-(9,9-dimethylfluoren-2-yl)pyrimidine (abbreviation: 6FL-4mDBTBPPm) represented by Structural Formula (121),respectively. Chemical formulae of materials used in this example areshown below.

<<Fabrication of Light-Emitting Element 3 and Light-Emitting Element 4>>

First, indium tin oxide containing silicon oxide (ITSO) was depositedover the glass substrate 1100 by a sputtering method, so that the firstelectrode 1101 which functions as an anode was formed. The thickness was110 nm and the electrode area was 2 mm×2 mm.

Next, as pretreatment for forming the light-emitting element over thesubstrate 1100, the surface of the substrate was washed with water,baked at 200° C. for 1 hour, and subjected to UV ozone treatment for 370seconds.

After that, the substrate 1100 was transferred into a vacuum evaporationapparatus where the pressure had been reduced to approximately 10⁻⁴ Pa,and subjected to vacuum baking at 170° C. for 30 minutes in a heatingchamber of the vacuum evaporation apparatus, and then the substrate 1100was cooled down for about 30 minutes.

Next, the substrate 1100 was fixed to a holder provided in the vacuumevaporation apparatus so that a surface of the substrate 1100 over whichthe first electrode 1101 was formed faced downward. In this example, acase is described in which the hole-injection layer 1111, thehole-transport layer 1112, the light-emitting layer 1113, theelectron-transport layer 1114, and the electron-injection layer 1115which are included in the EL layer 1102 are sequentially formed by avacuum evaporation method.

After reducing the pressure of the vacuum evaporation apparatus to 10⁻⁴Pa, 1,3,5-tri(dibenzothiophen-4-yl)benzene (abbreviation: DBT3P-II) andmolybdenum(VI) oxide were deposited by co-evaporation with a mass ratioof 4:2 (=DBT3P-II (abbreviation): molybdenum oxide), so that thehole-injection layer 1111 was formed over the first electrode 1101. Thethickness of the hole-injection layer 1111 was 20 nm. Note thatco-evaporation is an evaporation method in which a plurality ofdifferent substances are concurrently vaporized from respectivedifferent evaporation sources.

Then, 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation:BPAFLP) was deposited by evaporation, whereby the hole-transport layer1112 was formed. The thickness was 20 nm.

Next, the light-emitting layer 1113 was formed over the hole-transportlayer 1112.

In the light-emitting element 3, the light-emitting layer 1113 with astacked-layer structure was formed to have a thickness of 40 nm bydepositing 6Ph-4mDBTBPPm-II (abbreviation),N-(1,1′-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine (abbreviation: PCBBiF), and(acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III)(abbreviation: [Ir(tBuppm)₂(acac)]) by co-evaporation to a thickness of20 nm with a mass ratio of 6Ph-4mDBTBPPm-II (abbreviation) to PCBBiF(abbreviation) and [Ir(tBuppm)₂(acac)] (abbreviation) being0.7:0.3:0.05, and then depositing 6Ph-4mDBTBPPm-II (abbreviation),PCBBiF (abbreviation), and [Ir(tBuppm)₂(acac)] (abbreviation) to athickness of 20 nm with a mass ratio of 6Ph-4mDBTBPPm-II (abbreviation)to PCBBiF (abbreviation) and [Ir(tBuppm)₂(acac)] (abbreviation) being0.8:0.2:0.05.

In the light-emitting element 4, the light-emitting layer 1113 with astacked-layer structure was faulted to have a thickness of 40 nm bydepositing 6FL-4mDBTBPPm (abbreviation), PCBBiF (abbreviation), and[Ir(tBuppm)₂(acac)] (abbreviation) by co-evaporation to a thickness of20 nm with a mass ratio of 6FL-4mDBTBPPm (abbreviation) to PCBBiF(abbreviation) and [Ir(tBuppm)₂(acac)] (abbreviation) being0.7:0.3:0.05, and then depositing 6FL-4mDBTBPPm (abbreviation), PCBBiF(abbreviation), and [Ir(tBuppm)₂(acac)] (abbreviation) to a thickness of20 nm with a mass ratio of 6FL-4mDBTBPPm (abbreviation) to PCBBiF(abbreviation) and [Ir(tBuppm)₂(acac)] (abbreviation) being0.8:0.2:0.05.

Note that in each of the light-emitting element 3 and the light-emittingelement 4 in this example, exciplex formation in the light-emittinglayer is possible.

Then, in the light-emitting element 3, 6Ph-4mDBTBPPm-II (abbreviation)was deposited by evaporation to a thickness of 15 nm over thelight-emitting layer 1113 and bathophenanthroline (abbreviation: Bphen)was then deposited by evaporation to a thickness of 15 nm, whereby theelectron-transport layer 1114 having a stacked-layer structure wasformed. In the light-emitting element 4, 6FL-4mDBTBPPm (abbreviation)was deposited by evaporation to a thickness of 15 nm over thelight-emitting layer 1113 and bathophenanthroline (abbreviation: Bphen)was then deposited by evaporation to a thickness of 10 nm, whereby theelectron-transport layer 1114 having a stacked-layer structure wasformed.

Furthermore, lithium fluoride was deposited by evaporation to athickness of 1 nm over the electron-transport layer 1114, whereby theelectron-injection layer 1115 was formed.

Finally, aluminum was deposited by evaporation to a thickness of 200 nmover the electron-injection layer 1115 to form the second electrode 1103serving as a cathode; thus, the light-emitting element 3 and thelight-emitting element 4 were obtained. Note that in all the aboveevaporation steps, evaporation was performed by a resistance heatingmethod.

Table 3 shows element structures of the light-emitting element 3 and thelight-emitting element 4 obtained through the above-described steps.

TABLE 3 Hole- Hole- Light- Electron- First injection transport emittinginjection Second electrode Layer Layer Layer Electron-transport LayerLayer Electrode Light- ITSO DBT3P-II: BPAFLP * ** 6Ph-4mDBTBPPm-II BphenLiF Al emitting (110 nm) MoO_(x) (20 nm) (15 nm) (15 nm) (1 nm) (200 nm)Element 3 (4:2 40 nm) Light- ITSO DBT3P-II: BPAFLP *** ****6FL-4mDBTBPPm Bphen LiF Al emitting (110 nm) MoO_(x) (20 nm) (15 nm) (10nm) (1 nm) (200 nm) Element 4 (4:2 40 nm) *6Ph-4mDBTBPPm-II:PCBBiF:[Ir(tBuppm)₂(acac)] (0.7:0.3:0.05 20 nm) **6Ph-4mDBTBPPm-II:PCBBiF:[Ir(tBuppm)₂(acac)] (0.8:0.2:0.05 20 nm) ***6FL-4mDBTBPPm:PCBBiF:[Ir(tBuppm)₂(acac)] (0.7:0.3:0.05 20 nm) ****6FL-4mDBTBPPm:PCBBiF:[Ir(tBuppm)₂(acac)] (0.8:0.2:0.05 20 nm)

Further, the fabricated light-emitting elements 3 and 4 were sealed in aglove box containing a nitrogen atmosphere so as not to be exposed tothe air (specifically, a sealant was applied onto an outer edge of theelement and heat treatment was performed at 80° C. for 1 hour at thetime of sealing).

<<Operation Characteristics of Light-Emitting Element 3 andLight-Emitting Element 4>>

Operation characteristics of the fabricated light-emitting elements 3and 4 were measured. Note that the measurement was carried out at roomtemperature (in an atmosphere kept at 25° C.).

FIG. 24 shows current density-luminance characteristics of thelight-emitting elements 3 and 4, FIG. 25 shows voltage-luminancecharacteristics thereof, FIG. 26 shows luminance-current efficiencycharacteristics thereof, and FIG. 27 shows voltage-currentcharacteristics thereof.

FIG. 26 reveals that the light-emitting element 3 and the light-emittingelement 4, which use the heterocyclic compounds of embodiments of thepresent invention in the light-emitting layers and theelectron-transport layers, have reduced power consumption and highefficiency.

Table 4 shows initial values of main characteristics of thelight-emitting elements 3 and 4 at a luminance of about 1000 cd/m².

TABLE 4 External Current Current Power Quantum Voltage Current DensityChromaticity Luminance Efficiency Efficiency Efficiency (V) (mA)(mA/cm²) (x, y) (cd/m²) (cd/A) (lm/W) (%) Light- 2.8 0.032 0.81 (0.41,0.58) 740 92 100 24 emitting Element 3 Light- 2.8 0.043 1.1 (0.39, 0.60)1200 110 120 28 emitting Element 4

The above results in Table 4 also show that the light-emitting elements3 and 4 fabricated in this example have high luminance and high currentefficiency.

The light-emitting element 4 was subjected to a reliability test. FIG.28 shows results of the reliability test. In FIG. 28, the vertical axisindicates normalized luminance (%) with an initial luminance of 100% andthe horizontal axis indicates driving time (h) of the element. Note thatin the reliability test, the light-emitting element 4 was driven underthe conditions where the initial luminance was set to 5000 cd/m² and thecurrent density was constant. The light-emitting element 4 kept about83% of the initial luminance after 100 hours elapsed.

The results of the reliability test showed that the light-emittingelement 4 has high reliability. In addition, it was confirmed that withthe use of the heterocyclic compound that is one embodiment of thepresent invention, a light-emitting element with a long lifetime can beobtained.

This application is based on Japanese Patent Application serial no.2012-172801 filed with Japan Patent Office on Aug. 3, 2012, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. An organic compound represented by a formula(G1):

wherein Ar¹ to Ar³ separately represent hydrogen, an alkyl group having1 to 4 carbon atoms, a substituted or unsubstituted phenyl group, or asubstituted or unsubstituted biphenyl group, wherein R¹ to R³ separatelyrepresent hydrogen, an alkyl group having 1 to 4 carbon atoms, or asubstituted or unsubstituted aryl group having 6 to 13 carbon atoms,wherein α represents a substituted or unsubstituted phenylene group,wherein n is 2 or 3, and wherein Z represents oxygen or sulfur.
 2. Theorganic compound according to claim 1, wherein the organic compound isrepresented by a formula (G2):


3. The organic compound according to claim 1, wherein the organiccompound is represented by a formula (100):


4. The organic compound according to claim 1, wherein the organiccompound is represented by a formula (101):


5. A light-emitting element comprising the organic compound according toclaim 1, wherein the light-emitting element further comprises a layerbetween a pair of electrodes, and wherein the layer comprises theorganic compound.
 6. A light-emitting element comprising the organiccompound according to claim 1, wherein the light-emitting elementfurther comprises: a layer between a pair of electrodes, the layercomprising: the organic compound; an aromatic amine; and aphosphorescent compound, wherein a combination of the organic compoundand the aromatic amine is configured to form an exciplex.
 7. Thelight-emitting element according to claim 6, further comprising anelectron-transport layer between the layer and one of the pair ofelectrodes, wherein the electron-transport layer comprises the organiccompound.
 8. A light-emitting device comprising the light-emittingelement according to claim
 6. 9. An electronic device comprising thelight-emitting device according to claim
 8. 10. A lighting devicecomprising the light-emitting device according to claim
 8. 11. Alight-emitting element comprising: a layer between a pair of electrodes,the layer comprising: an organic compound comprising a pyrimidine ring;an aromatic amine; and a phosphorescent compound, wherein a combinationof the organic compound and the aromatic amine is configured to form anexciplex.
 12. The light-emitting element according to claim 11, whereinthe organic compound further comprises a ring including a hole-transportskeleton.
 13. The light-emitting element according to claim 11, whereinthe organic compound has a molecular weight greater than or equal to 400and less than or equal to
 1200. 14. The light-emitting element accordingto claim 12, wherein the ring including the hole-transport skeleton is acarbazole ring, a dibenzothiophene ring, or a dibenzofuran ring.
 15. Thelight-emitting element according to claim 11, wherein the aromatic aminecomprises a pyrimidine skeleton.
 16. A light-emitting device comprisingthe light-emitting element according to claim
 11. 17. An electronicdevice comprising the light-emitting device according to claim
 16. 18. Alighting device comprising the light-emitting device according to claim16.